根据首字母填写英语单词。

1. Eating a b_____ diet is also very important.

2. Last night he had a s_____ because he ate something bad.

3. I'd love to, but I have to b_____ my little sister.

4. Thank you for your i_____.

5. She is a good listener because she can keep all the s_____.

信息系统开发的经验表明，系统出现的错误中有60％～80％是来源于（ ）。

A．需求定义

B．系统设计

C．系统运行

D．程序维护