3. My daughter by my parents.
• To look after
• Had been looking after
• Was being looked after
• Looked after

The correct choice is "was being looked after".

Explanation:

"My daughter to look after by my parents" is an unclear sentence. "To look after" is missing the verb, as in what the daughter or the parents were doing.

 "Had been looking after" is not in the correct tense as the sentence includes "by".

"Looked after" would be correct if the the "by" was not in the sentence. Because "by" is included in the sentence, the parents are doing something to the daughter. Therefore saying that "my daughter looked after" cannot work.