这几道题为什么这么选1 There are four _____ and two _____ at the _____

这几道题为什么这么选
1 There are four _____ and two _____ at the _____
A Johns, Marys, doctors
B Johns, Marys,doctor's
C John's, Mary's, doctor's
D John, Mary, doctor's
选B
2 My sister,an inexperienced rider, was found sitting on the bicycle______ to balance it.
A having tried B trying
C to try D tried
选 B
3 He insisted that he should _____ the English lesson because his English was rather poor
A join B take C give D get
选B
5 Modern equipment and no smoking are two of the things I like ____
working here.
A with B over C at D about
选D
为什么这么选啊