A complex sentence is a sentence which is comprised of an independent and a dependent clause. The independent clause is a clause which is complete in itself. It does not require any other support to provide a sense. A dependent clause is a clause which does not provide the complete sense, although the subject and the verb is contained in it. In the above sentence 'Mary likes to relax by hiking in the woods' is the independent clause and 'which is also a great way to exercise' is the dependent clause.
