she ___babysit her sister and help A need to B.must C.have to D.had to

题目

she ___babysit her sister and help A need to B.must C.have to D.had to
she ___babysit her sister this weekend.A need to B.must C.have to D.had to

答案

选B.
句子的意思是说,她这个周末要看孩子.
首先,this weekend就限定了时态,必须用将来时或现在时,因此不能选D.
再者,主语she是第三人称单数,因此动词应用第三人称单数形式,选A,应改为needs to,选C,应改为has to.
如果是情态动词的话,则不必考虑人称和数的变化.