1 A:inflexible
2 D:become extinct
3 B:end
4 D:compete
5 A:simple
6 C:fundamental
7 A: polluted
8 C:break
9 A:wiped
10 B:importance
11 C:undamaged
12 A:doubtful
13 D:approved
14 B:spread
15 B:cautious