⑴Where are your parents?____                           A. Yes, I'd like some fruit.

⑵Is your brother sleeping in the room?____      B. They are at home. 

⑶Can I help you?____                                         C. She's playing the piano.

⑷Would you like some fruit?____                       D. No, I'm not.

⑸Can you see the red light?____                        E. She's singing.

⑹What is Helen doing?____                                F. Yes, please.

⑺Are you busy?____                                           G. No, I can't.

⑻What is she doing in the music room?____     H. No, he isn't.

全球气候变暖是目前世界最主要的环境问题。全球气候继续变暖的后果，会使全球降水量重新分配、冰川和冻土消融、海平面上升等，既危害自然生态系统的平衡，更威胁人类的食物供应和居住环境。从本质上来说全球气候变暖属于环境问题中的（     ）