A．Because she needed to care for the children.

　　B．Because she remembered the previous thing.

　　C．Because she wanted the author to read for her.

　　D．Because she was unwilling to live with the author.

　　【解析】　细节理解题。根据最后一段中的"Finally，great tears rolled down her face and she cried，'...That time and that Christmas have been a burden on my heart for twenty­five years.I wish your dad were here so I could tell him how sorry I am for what I said.'"可知，母亲想起了以前圣诞节的事，对自己所做的事感到难过，因此无法入眠，故B项正确。

　　【答案】　B

　　4．What is likely to be described in the next paragraph?

　　A．How they would celebrate the Christmas.

　　B．How the author's father supported the family.

　　C．What happened to the author's parents in the past.

　　D．The reason for the author's parents' divorce.

　　【解析】　根据最后一段母亲所说的话"That time and that Christmas have been a burden on my heart for twenty­five years.I wish your dad were here so I could tell him how sorry I am for what I said"可推知，母亲想起了以前圣诞节的事，对自己所做的事感到难过；据此可以判断，下文将叙述发生在作者父母身上的故事，故C项正确。

　　【答案】　C

　　B

　　Sleep scientist Ying­Hui Fu at the University of California, San Francisco, says "We do not know why some humans need more sleep；why some humans need less sleep；why, when we do not sleep, we do not function well.We just do not know much about sleep at all." But scientists now know: A team led by Professor Fu has reported the first genetic link to how much sleep we need.

The team was looking for a natural clock in the body that controls sleep and