>>347
疑問形にする必要がない
先の表現を借りると
A type of detective story in which the focus is "how they have done it".
A type of detective story in which the focus is "why they have done it".
ということだ

>>348
辞書に載っている
英和辞典なんかじゃなく英英辞典を引け
whydunit:
A type of detective story in which the focus is not on who committed the crime, but what were their motives for committing it.