An action verb refers to an action, that is not a state. Verbs which are NOT action verbs are all verbs of states, most typically the verb "to be". So sentences with the verb "to be" are likely not to contain action verbs: here they're options A C and D - those don't use an action verb.
The correct answer is B. We bought some vegetables for our salad.
and the action verb is: "bought".
