Which of the Following Is NOT a Disadvantage of the Individual

Which of the following is NOT a disadvantage of the individual matching?

A) it is often difficult to decide which of the many possible extraneous variables one should control through matching.
B) the more variables on which one wishes to match participants, the more difficult it is to find matched participants.
C) it is often difficult to arrange for two participants to arrive at the experimental site at the same time.
D) this type of matching limits the generality of your results to a unique group of participants