The correct option is
C Time
In order to identify the type of adverb, let's understand what adverbs are. Adverbs are words that describe something about the verbs. For example, I ran fast. Here, 'fast' describes the way 'I' ran, so 'fast' is an adverb.
Option A - 'Manner' describes the way an action is done. Here, the adverb 'before' doesn't describe the way the action was done. Hence, option A is incorrect.
Option B - 'Place' describes the place where the action took place. Here, the adverb 'before' doesn't describe the place where the action was done. Hence, option B is incorrect.
Option D - 'Frequency' describes the duration or the number of times the action was done or takes place. Here, 'before' doesn't describe the number of times the action was done. Hence, option D is incorrect.
Option C - 'Time' describes when the action was/is/will be done. Here, 'before' describes when the action was done. Hence, option C is the correct answer.
'Before' explains the time the subject 'met' the object in the given sentence.