"X" is mitochondria . Mitochondria generates energy to make the sperm to move its tail.
If “X” is not in the sperm, fertilisation might not occur because sperm has no energy to swim to the ovum.
解释:mitochondria 为精子产生能量,以便它可以游向ovum,进而发生fertilisation。如果没有mitochondria,精子就没有能量游向ovum,就不会发生fertilisation.
我觉得那你的答案(“X” is a muscle cell, muscle cell make the sperm to move its tail.)不能拿分。第一,muscle cell 不是正确的答案。第二,你没有回答到第二个问题(If “X” is not in the sperm, what might happen to fertilization process?)。