Two Populations of Snails Are Allopatric, Living in Areas That

Two populations of snails are allopatric, living in areas that have different soil compositions.The snails are not very mobile.Researchers are interested in whether the populations have acquired different types of reproductive isolation.Which would best determine if they are undergoing have mechanical isolation?

A) Examine the genitalia of males and females of the different populations. If male genitalia of one population fit well with the female genitalia of the other, then they likely have mechanical isolation.
B) Examine the genitalia of males and females of the different populations. If male genitalia of one population do not fit well with the female genitalia of the other, then they likely have mechanical isolation.
C) Bring them into the lab. Observe single pairs of a male from one population and a female from the other. If they mate, then they exhibit mechanical isolation.
D) Bring them into the lab. Observe single pairs of a male from one population and a female from the other. If they do not mate, then they exhibit mechanical isolation.
E) Observe when each population is active. If they are active at the same time, then they exhibit mechanical isolation.