Should only be preceded by another complex sentence.
Should only be followed by another complex sentence.
Has more than one phrase.
Has only one phrase.

Those are poorly worded choices, but the answer would have to be the "has more than one phrase'.

See these (http://www.google.com/search?num=100&hl=en&lr=&newwindow=1&safe=off&oi=defmore&defl=en&q=define:Complex+sentence).