几道英语选择题,麻烦理由啊!

几道英语选择题,麻烦理由啊!
1.mr.brown,some students want to see you.__wait here or outside?
a.should
b.will
c.shall
d.are
2.tom must have been here just now,__?
a.did not he
b.was not he
c.has not he
d.isn not he
3.if you really want to be in good health,you should ___always___so much
a.not,be smoking
b.not,have smoked
c.not,to smoke
d.be not,smoking
(test11)
第二第三答案应该是BA,但是不知道理由,1楼2楼你们的答案错了