Analyze: what is global warming? how is it caused?

Its the heating of thew planet it is caused because of all the gases we put into the air

The answer is D. Hearing these words from his mother made Gregor realise that the lack of any direct human communication, along with the monotonous life led by the family during these two months, must have made him confused — he could think of no other way of explaining to himself why he had seriously wanted his room emptied out.