It’s the gases natural gas and the burning of coal give off add to the overheating of the earth.
A. that; what
B. that; that
C. which; which
D. that; which
网友回答
A. that; what
(答案→)B. that; that
C. which; which
D. that; which
解析：考查从句。第一个为定语从句，且先行词在定语从句中充当宾语，故用that或which；第二格是强调句的后半句，故用that。意为：是天然气和煤放出的气体增加了地球的过热。