This is the 1058th most frequent Korean word.
조사에
"조사에" means "in the investigation" or "in the survey," depending on context.
Here, '조사에' (in 조사에 몰두하다) indicates that the subject is deeply engrossed in a particular investigation or research.
그는 과학적 조사에 몰두하고 있어요.
He is immersed in scientific research.
In this context, '조사에' (in 범죄 조사에 필요한) describes the context or purpose related to the investigation.
범죄 조사에 필요한 증거를 찾았습니다.
The evidence needed for the crime investigation was found.
Here, '조사에' (in 설문 조사에 응답하다) refers to participation in the specific survey mentioned.