Subordinating conjunctions are transitions words that signal:

Subordinating conjunctions are transition words that signal the beginning of a subordinating clause. (A subordinate clause is a clause that depends on another clause and cannot stand alone.)

Examples of subordinating conjunctions are:

because, when, as, as long as, unless, until, after, before, although, provided that, etc.

There are 3 types of conjunctions:

The subordinating conjuctions can introduce:

martians or other types of aliens represent a unique fear as opposed to zombies. vampires and other types of monsters.   in most sci-fi stories, aliens come from other worlds and have different or more advanced technology.   abductions and experimentation on human bodies that involve these technologies, or the use of these technologies against human beings and the use of unknown "powers", are a type of fear that's different from that of other types of monsters.