- The detective looked into the murder.
1a. The detective looked into the murder case.
- Please look into the matter.
2a. Please look in the matter.
- He jumped into the river.
3a. He jumped in the river.
- He jumped into the pool.
4a. He jumped in the pool.
Please choose the right sentences.
I find 1,2,3 and 4 to be marginally better. If you’re already in the river, and you start jumping (which would require a shallow river), you’re jumping in the river, but jumping into the river indicates that you are entering the water. Like I said, it’s pretty marginal. If you say “in”, most people will assume that it’s a jump into.