The correct answer is B) were swimming.
A) Samuel and Thomson was swimming in the ocean. Doesn't sound right.
B) Samuel and Thompson were swimming in the ocean. Ding ding ding. Correct.
C) Samuel and Thompson is swimming in the ocean. This would be correct if it were 'are swimming'.
D) Samuel and Thompson be swimming in the ocean. Nowadays this is correct, but it is technically incorrect. Don't say it unless you're from the hood or are a gangster.
