根据课文内容填空。

      David has a 1.b          day on 2.T         . He 3.g____  up at 6:30. He has 4.l         at 5.a____

 to twelve. After 6.___   , he goes to the 7.          and cleans it carefully. At 4:15, he 8.          to  

watch a 9.f          game. After supper, he should do10.         11.        . He is 12.r___  _busy today.

最多可容纳8个电子的壳层是（）

A.K层

B.L层

C.M层

D.N层

E.O层