Neha : When Did you get this book?

Sheela : Yesterday morning.

The response ‘Yesterday morning’ denotes a point of time, thus the appropriate question word here is ‘When’ which is used to enquire about the time of action.

Neha : Why is your sister crying?

Sheela : Because she has lost her doll.

The response phrase begins with the word ‘because’ stating the reason, thus the appropriate question word here is ‘Why’ which is used to enquire about reason of the action.

Neha : Whose Room is this, yours or hers?

Sheela : It’s ours.

The response phrase ‘it is ours’ denotes possessiveness, thus the appropriate question word here is ‘Whose’ which is used to enquire about the relation of the object to the subject.

Neha : How do you go to school?

Sheela : We walk to school. It is nearby.

The response ‘We walked’ denotes manner, thus the appropriate question word here is ‘How’ which is used to enquire about the manner of the action.