The sentence "Australia's rain forests are located in the northeast" is composed of a subject "Australia's rain forests" and a predicate "are located in the northeast" (verb and other details that complete an idea). This means this sentence only contains one clause (subject-verb/predicate unit) and due to this, it is classified as a simple sentence. Indeed, compound or complex sentences should contain two or more clauses but in simple sentences, there is only one clause or grammatical unit that is complete and expresses an idea.
