Select the word that means releases for use. The body's immune system fights off infections to help the body stay healthy. When bacteria or viruses invade, the immune system first identifies them as threats. If these invaders appear dangerous, the immune system mobilizes the appropriate forces and sends them to attack. White blood cells surround, ingest, and kill the infection. Once it is under control, the immune response ends, and most of the white blood cells self-destruct. A certain number will remain as memory cells, to be prepared for the next infection.

sentences vary by structure as well as by function. there are compound, complex, and compound-complex sentences.

simple sentence

i like to read.

a simple sentence has one independent clause.

compound sentence

i like to read, and i also like to write.

a compound sentence includes more than one independent clause, connected by a coordinating conjunction (and, but, for, nor, or, so, or yet).

complex sentence

i prefer to read books that are bestsellers.

a complex sentence includes one independent clause and one or more dependent clauses. (a dependent clause is one that cannot stand alone.) types of dependent clauses include relative clauses (i kicked the boy who pinched me), adverb clauses (i am going home now because i have a curfew), and noun clauses (i don't know what to do next).

compound-complex sentence

although i prefer to read current bestsellers, i do like to read old agatha christie mysteries, and i also like some 20th-century science fiction.

compound-complex sentences take a bunch of clauses (multiple independent clauses, and one or more dependent clauses) and toss them together like a salad. although these sentences take practice to write in a grammatically correct fashion, they can hold a tremendous amount of meaning, and are common in academic writing.

tessa’s film suffers when she refuses to deviate from her plan as obstacles arise.