What's Happened? - Perfect Tense Forms

'... have walked ... ' expresses affirmative past action. The 'often' goes most naturally in the middle of the phrase; at the heart of it.
Sometimes in English, if you are boasting a bit about all the places you have been and things you have done, someone may say: 'Been there, done that, got the tee-shirt!'. This means that they HAVE (themselves, too) already done all these things. Like many other languages, English uses the 'have'-auxiliary to express what someone HAS done ... because their past experience is something that belongs to them and makes them the person they are, so they 'have' it in a similar way to 'having' a dog or 'having' a certain car or 'having' an official piece of paper to prove what they 'have' achieved (like an exam result, maybe a university degree, or that they passed their Driving Test).
Meanwhile, the show 'My Fair Lady' is all about a poor London girl who learns to speak 'proper English'. You might enjoy watching it, to work on your accent, too; and there are lots of splendid songs in it ('Get me to the church on time', 'I could have danced all night' and many, many others)!

Any of these are possible, except Answer 1 ('has' is singular), but Answer 4 is the strongest. It suggests that they have only just stopped, or maybe that they interrupted to tell you this, and they might quite like to carry on and play some more.

These are all OK (from the English point of view) except Answer 2 which is incomplete, although it would probably be understood.
But Answer 4 gives the clearest suggestion that it happened very recently ~ so someone might do something about it quickly, for instance, before the floor is permanently damaged or the carpet stained.
Compare the shape of ' ... has just been ... ' with ' ... have often walked ... ' in Question 1.

This is how to make a simple past question in English: many other European languages do likewise, by just turning-round the pronoun and the auxiliary verb:
Answer: 'I have finished' ('J'ai fini' / 'Ich habe geendet, ich bin fertig' , etc.)
Question: 'Have you finished?' ('Avez-vous fini?' 'Bist du fertig?' ...)
We hope you do not find yourself in an embarrassing situation like this if you are staying in a British household!

The order here is always:
Question-word + have/has + [subject] + past verb
e.g. 'Where have they taken the prisoner?' 'Why has she gone to the doctor?'
If we are referring to an action a bit longer ago ~ a bit further in the past, but whose effects are still true ~ we can use a similar-shaped structure:
'When did he get that haircut?' 'Who did you meet after church?'

Answer 3 is also possible. We use the 'have [done]' form of a verb when explaining when something began in the past, to show how long it has been going on. In your own language you may be more familiar with using the present tense for this ~ for the perfectly logical reason that the action is still happening.
One of the most obvious signs of a non-native English speaker is when they say e.g. 'I am learning English since last year', or even just 'I learn it ...'. If you say this, people will understand you, and they will allow for you having limited experience of the language; but that doesn't mean that either of these expressions was strictly a correct form.

English does not usually use the 'have + [verb]ed' form of the past, if the time of the action is already clearly in the past.
'Last year I went ...' 'In Roman times they did ... ' etc.

Again, the adverb (in this case, the negative 'never') fits between the 'has/have' and the main part of the verb.

Here, the situation is that the bag has disappeared, so it is some time since you saw it. In such circumstances we refer to a 'closed' form of the past (i.e. things have changed, and can no longer be treated the same), so we ask 'When did you ... ?' 'How did you ... ?' and 'Why did you ..?' -type questions.

Well, if you 'have had enough' ~ so have we!
Please try these again if you need to, else carry on to some other Quiz.