591.She will tell us why she feels so strongly that each of us has a role ________ in making the earth a better place to live.
A.to have played
B.to play
C.to be played
D.to be playing
592.Don't use words,expressions,or phases _______ only to people with specific knowledge.
A.being known
B.having been known
C.to be known
D.known
591.答案是B;短语play a role/part in (doing)sth.在（干）某事中起作用。此题中to play作定语修饰前面的a role。
592.答案是D;此处known作定语修饰前面的名词。Be known to sb.为…所知。
