5. Everyone should make a contribution to (protect) the environment.
[指点迷津]
look forward to+名词/代词/doing意为“期待、盼望”,该短语中的to为介词。类似用法的还有:give one’s life to doing
sth.“献身于做某事”;pay attention
to doing sth.“注意做某事”;make a
contribution to doing sth.“为某事做贡献”;be used to doing sth.“习惯于做某事”等。