13.—Who do you think has eaten my cake, father?—It( ) beyour younger sister.
A、must
B、should
C、will
D、may
二、词汇与语法知识: 共15小题; 每题2分, 共30分。从每小题的四个选择项中, 选出最佳的一项。6.Of all( )reasons for my decision to become a university professor, my father's advicewasmost( )important one.