I really ______ go back to work tomorrow, but I feel so ill that

I really ______ go back to work tomorrow, but I feel so ill that I've decided to stay in bed for a few more days.
A、ought to
B、can
C、might
D、may
【正确答案】：A
【题目解析】：ought to的意思是“应当，应该"，与题意相符。答案为A。