The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
Single cysticercus is spherical, measuring 1–2 cm in diameter. The central space is filled with fluid like a bladder, hence it is also called bladder worm. It is characterised by large vesicle and contains an invaginated protoscolex. Therefore, Assertion and Reason are correct and Reason is the correct explanation for Assertion. Hence, option A is correct.