国家开放大学 / 综合英语（2）
正确率：100%
No one saw Richard get into the house because _ _ _ _ .
a.it was night time
b.he ran very fast
c.he stood behind a tree
d.he was very clever
a.it was night time
b.he ran very fast
c.he stood behind a tree
d.he was very clever
参考答案：