People should think about they can have a positive influence on the planet.
A. why
B. that
C. what
D. how
网友回答
A. why
B. that
C. what
(答案→)D. how
解析：考查宾语从句。 宾语从句How they can have a positive influence on the planet作为think about的宾语。本句主要是从句意出发。句意：人们应该考虑他们怎么样才能对地球有积极的影响。