The word "it" (Para. 4, the last sentence) refers to ______.

A．feel they are mistreated because of limited knowledge of English
B．are afraid that their academic successes bear a strong Asian character
C．still worry about unfair treatment in society
D．generally feel it a shame to have to depend on their parents

A．it enables us to survive in the closed system of a spaceship
B．it is a modern science that everybody has to learn
C．it can be learned quickly if we study it hard
D．it helps us to understand the relationship between living beings and the environment