Grammar help

[Joekage]

今度の飛行機事故の＿　＿　★ ＿が調べている
１　調査委員会　２　原因　３　くわしく　４　につい て

The answer for the star is 3. There is something wrong with this exercise. くわしく is an adverb but there is no verb come before it.

[RadioKid]

The expected answer would be "今度の飛行機事故の原因についてくわしく調査委員会� �調べている。". This is not wrong.

However, this is not natural. As "くわしく:KUWASHIKU;in detail" is adverb, it decorates the verb "調べている:SHIRABETEIRU; is investigating", "KUWASHIKU" should be near the verb.

I would say "今度の飛行機事故の原因について、調査委員会が詳し� �調べている。".

[Joekage]

Thank you!