题干
—Did you have any difficulty catching yesterday’s lecture?
—No. The professor spoke very clearly to make his speech easy _____.
—No. The professor spoke very clearly to make his speech easy _____.
A：understood
B：understanding
C：to be understood
D：to understand
答案(点此获取答案解析）
D
是某单炔烃与氢气加成后的产物，则此炔烃可能有