B subordinate clause includes a subject and a verb, can't stand alone in a sentence because it doesn't convey a complete idea. But in order for it to form a complete idea, a subordinate clause MUST BE combined with an independent clause. It can be attached before or after the subordinate clause. An Independent clause can stand alone in a sentence and it's a complete sentence. Hence "Independent" meaning can survive alone
therefore, which clause is underlined?
but here's what you should know
"Steve is going downtown so that he can buy some sneakers."