As may be used as a relative pronoun when such stands in the main clause.
They have, therefore, a logical dependence on the main clause.
Two or more subordinate clauses may be attached to the main clause separately, each as a distinct modifier or complement.
It is presupposed that he can readily identify the main clause itself.
The complex sentence has only one main clause and one or more dependent clauses.
It admits (or concedes) some fact or supposition in spite of which the assertion in the main clause is made.
The other clauses make sense only when they are united with the main clause.
The main clause is the same as in the first (the polar bear sometimes reaches temperate latitudes).
Rescue this main idea, express it in the main clause, and if possible subordinate the rest of the sentence to it.
A complex sentence may be expanded either by compounding the main clause, or by increasing the number of subordinate clauses.