The correct option is A If both the assertion and the reason are true and the reason is a correct explanation of the assertion
Each sperm of Riccia is a minute, slender curved structure. It is furnished with a pair of whiplash flagella at its anterior end. The sperms do not leave the antheridium unit enough moisture is present to permit them to swim about. Several of the sperms may swim downward in the liquid in the neck.