In the context of the passage, which of the following options would best replace the underlined portion of sentence 17 (reproduced below) ? Even if scientists do find liquid water someday, they better be darned sure they don’t contaminate it with microorganisms from Earth.

A. we all better hope that they don’t go and contaminate it

B. hopefully they won’t mess it up by contaminating it

C. let’s hope that they don’t go and contaminate it

D. they will have to be careful to avoid contaminating it

E. it better not get contaminated by them