问题补充:
the sentence , so he asked the teacher to explain it again.
A. Not having understood
B. As he didn’t understand
C. Having not understood
D. He didn’t understand
答案:
A. Not having understood
B. As he didn’t understand
C. Having not understood
(答案→)D. He didn’t understand
解析:句意:他不理解这个句子,所以他请求老师再解释一次。选项AC都是非谓语动词,因为整个句子已经有并列连词so,所以前后应该都是句子,故排除ABC,故选D。