保护层的性能应满足（）的要求。

A.抗大气腐蚀

B.不燃烧、不开裂

C.密度大

D.反辐射性能好

E.使用寿命长

根据句意或中英文提示写出句中所缺单词。（共5分）

1.Sandy doesn’t go to school today b__________ she is ill.

2.We will have supper at my __________ (爷爷奶奶) home.

3.Those old men and women do morning __________（锻炼）every day.

4.Our first lesson usually __________（begin）at 7:25am every day.

5. __________ comes before Thursday.