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
网友回答
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。