Question

date - rape drugs are difficult to detect because they can be
o kept in a backpack
o used by a stalker
o given by private therapists
o mixed with food or drink

Explanation:

Date - rape drugs are often difficult to detect because they can be surreptitiously mixed with food or drink, making it hard for the victim to notice before it's too late. They are not typically given by private therapists, just being used maliciously often by stalkers or attackers in the context of date - rape scenarios, and being kept in a backpack is not related to their detectability.

Answer:

mixed with food or drink