单选题，答案是什么，为什么其它不行，谢谢...
11.The manager insisted that the plan __________ reasonable and we __________.
A. was , carry it out B. were , carried it out
C. was , carried it out D. be , carry it out

12.The students were standing in front of the swimming pool ,__________ swimming suits .
A. all were wearing B. all wearing
C. all of them wore D. all of whom wearing

16.He made a promise ___________ he would help me.
A. what B. when C. that D. which

19.He didn’t know _________ or stay.
A. to leave B. if to leave C. whether leave D. whether to leave

11.The manager insisted that the plan __________ reasonable and we __________.
A. was , carry it out B. were , carried it out
C. was , carried it out D. be , carry it out

A
前面是“坚持认为”，不用虚拟语气；后面是“坚持”，要用虚拟语气（省略了should）。判断是否要用虚拟语气，可以看句子是否包含了说话人对听话人主观意志的影响。本句中前面不包含，后面包含，所以选A.

12.The students were standing in front of the swimming pool ,__________ swimming suits .
A. all were wearing B. all wearing
C. all of them wore D. all of whom wearing

B
were是这句话的谓语动词，中间用逗号连接，所以后半句不能再出现谓语动词，排除AC.
若后面半句为定语从句，则从句中必然有谓语动词，所以不能说all of whom wearing， 而应该说all of whom were wearing。排除D。
选B，此句为独立主格结构。

16.He made a promise ___________ he would help me.
A. what B. when C. that D. which

C
固定用法，that引导同位语从句，其他皆不可。

19.He didn’t know _________ or stay.
A. to leave B. if to leave C. whether leave D. whether to leave

D
whether to do or （to） do 是固定用法
whether不能用if替换。