下列各句中，没有语病、表意明确的一项是（  ）

B

    John is an American boy. His family is in China now. John likes chocolates (巧克力) very much. But his mother doesn't give him any. They are not good for him, she thinks. But John has a very nice grandfather. The old man loves him very much, and sometimes he buys John some chocolates. Then his mother lets John eat them. She wants to make the old man happy. One Sunday evening John says in his room, "Please, God. Make them give me a big box of chocolates tomorrow. It's my birthday." His mother says, "God can't hear you, my boy." "I know, but my grandfather is in the next room. He can hear."

据报导：我国一家厂商制作了一种特殊的手机，在电池能耗尽时，摇晃手机，即可产生电能维持通话，摇晃手机的过程是将机械能转化为电能，如果将该手机摇晃一次，相当于将100g的重物举高40cm，若每秒摇两次，则摇晃手机的平均功率为（g=10m/s²）（   ）