Ronald ___ be ill at today .
A needn't B mustn't C isn't able to D can't
B 他今天一定不能生病.（角色重要,缺了不行）
i will come to see you if _______.
A you 're convenient .B it is convenient for you
C you feel convenient D it is convenient with you
D 固定用法,be convenient with,主语往往用it