完成句子：根据句意及汉语提示，用词组的适当形式填空。（每小题2分）

小题1:. Mrs. White is a kind woman. She spends most of her free time                    （照顾）these homeless dogs.

小题2:. There is                     (毫无疑问)that the engineer has made a mistake once again.

小题3:The boy’s parents are dead, so he has to                          （依靠）himself.

小题4:. Zheng He was the Ming Dynasty explorer whom all the Chinese people

（对……感到骄傲）.

小题5:. Now more and more persons walk or ride a bicycle to work                    （代替）driving a car.

计算机中存储器系统采用分层结构，其中价格最低、容量最大、速度最慢的是海量(后备)存储器，它主要用于存储大量存档或备份的信息。用来实现海量存储的除了光盘存储器外，通常还采用______存储器。