If I were you

Answer 4 is the correct traditional 'punchline' for this little jingle.
The skeleton of the structure is 'If .. were, ... would ... ' .
Answers 2 and 3 are more or less possible, but weak.

This example is set one stage further back into the past: 'something would have happened, if there had been the right circumstances'.

Answer 1 is also possible, but hints at some confusion about the tenses and timescales. 'You would never forget' suggests that nobody who attended the event would be able to erase it from their memory; the version in Answer 1 seems to be saying to one individual who HAD 'been there' that it is extraordinary / unbelievable / disappointing (etc.) that they HAVE in fact managed to forget.
Answers 3 & 4 set out with 'you was' which is not standard English, though you may well hear this formation in certain places and circumstances.

The person being spoken to here probably has expressed an interest; but 'were' is still correct, because the opportunity is theoretical, and even though they 'are' (Answer 2) / may be interested now, their attitude or circumstances may have changed by the time the offer materialises in the future.
'Was' may be heard in some comparable circumstances, but is a local / dialectal usage rather than 'proper English'.

This is a version of Question 3 that steps further into the past again: saying, in effect, that it's a pity the person being spoken to had not been at the event, because if they HAD, they would not have been able to forget it (but since they weren't there, obviously they can have no such memory).
Each of the 'distractor Answers' is either nonsensical or mis-formed, or both.

Answer 2 is 'the original' ; Answer 1 is possible, but doesn't carry the same emphasis about it now being too late to have known in advance ('If I had known') allowing time for the baking to happen in between.
The tense sequence in Answer 3 is plausible and understandable but nonetheless not correct English; Answer 4 (with its 'might') sounds very much less given to spontaneous generosity ('Had anyone bothered to make me aware that you might come, I supposed it could in theory have crossed my mind to bake something ... if I could be bothered, and happened to have the right ingredients ~ to save my needing to nip out specially for anything.').

Answer 1 is grammatically acceptable but stylistically unlikely (one can only go so far to avoid saying 'get' ... ); in Answer 3 the past progressive form is inappropriate, though it would probably be understood. Answer 4 is an acceptable and even stylish idiom, but it does not quite fit in this context. Its more usual use would be in such circumstances as :
'Given half the chance, he'd be off to the pub before the final whistle went.'
'Given good weather, we may manage to do that long hill-walk on Wednesday.'
In other words, 'Given ...' usually introduces a theoretical circumstance (in which the right conditions might indeed be 'given'), but not usually a situation in the past where it is now too late, as in this Question. For a theoretical, repeatable and/or habitual past circumstance ('Given a bone, the puppy would usually either chase it or chew it') it works fine, with a strong whiff of the Imperfect about it; but it won't do for a '1-off' that's now been missed.

This is a complex example but Answer 4 is fairly clearly the best.
'Wasn't' in Answer 1 is not Conditional; and surely, the second clause should be negative in this context?
Answer 2 works well apart from the silly mistake of writing 'of' instead of 'have' in the second clause (check the sense!).
'Couldn't be' in Answer 3 does not make very happy sense if the speaker actually IS sitting there saying it.

Answer 1 is surely too simple to be true!
We need two parallel conditions ( ' were / were ' ) and then 'would'. Remember that English does NOT require a second negative element after 'nothing ... ' (thus eliminating Answers 2 & 3).

This is more a matter of Modals, but seemed too splendid a quotation for us not to include it as this Quiz is written in the months running up to the centenary of the outbreak of World War One.
Specifically: we are looking for a single-syllable word here, in order not to spoil the rhythm at the very beginning of this poem (it's in Iambic Pentameter, like many classic Shakespeare passages: a 'di-DUM di-DUM di-DUM di-DUM di-DUM' rhythm that fairly obviously echoes the sound of a human heartbeat, such as each of us remember primally from when were still inside our mothers). So Answer 1 is 'out' on that basis, quite apart from its meaning.
Answer 2 is manifestly slightly stupid, since each of us will certainly die at some point (whether in battle or, we hope, more likely not) ~ so the clash of 'If' (suggesting something possible but uncertain) with 'shall' (a definite future intention) doesn't make comfortable sense. Similarly with the 'must' in Answer 4, which suggests a grim, ironic resignation: in which case, the poet might as well have written, 'SINCE I must die ...'. It is the very uncertainty that gives this poem its poignancy; and you can note from Brooke's dates that he himself did indeed die during the Great War.
The use of the 'should' is somewhat poetic but it is undoubtedly the right word here ... or as the French would have put it, in just such a 'foreign field' alongside the Somme or wherever, 'le mot juste'.