When and where to have a picnic yet

问题描述:

When and where to have a picnic yet
A are not decided
B has not decided
C have not been decided
D is not decided
yet不是完成时的标志么 那为什么不用完成时呢
d

知道了
when and where to have a picnic 这里是指一件事,所以是单数,而yet只是起一个强调“没有”的作用