Question

A complex sentence using the word Contribute

Answer 1

A complex sentence has a main clause and a dependant or subordinate clause right after, joining the two is subordinate conjunction.

Example:

You should always contribute to society since it will improve the lives of many people.

(You should always contribute to society) main clause.
(Since) subordinate clause
(Since it will improve the lives of many people)
dependent clause

Hope it helped. :D