Select the phrase/connector from the given three options which can be used to form a single sentence from the two sentences given below, implying the same as expressed in the statement sentences.
Case studies can provide circumstantial evidence that aerosols are carrying the virus. Researchers want to nail down how and when that happens.
1. but
2. and
3. hence
1
Only 1
2
Only 2
3
Only 3
4
Both 1 and 2
5
Both 2 and 3