问题补充:
halfway through the exercise, the teacher changed his mind and collected all our papers.
A. When only being
B. When we were only
C. Being only
D. Having been
答案:
A. When only being
(答案→)B. When we were only
C. Being only
D. Having been
解析:我们只做了一半练习老师就改变了主意把我们的试卷收了上去。因为主句与从句的主语不一致所以不能用分词做状语故选B