Which is a complex sentence?
a)
she shrieked at the sight of a broken window in her car.
b)
for two years the pustovas saved up enough money to go to disney world.
c)
terry knew that his wife was making dinner, but he ate an entire pie anyway.
eliminate
d)
once the company got onto the internet, the dale and thomas popcorn company quadrupled its business.

A complex sentence always includes a subordinate clause, which is a piece of information which is often added in using commas. The sentence will make sense if you remove the clause, and the subordinate clause is dependent on the main clause. This means that it won't make sense by itself.

Therefore, the correct answer is D because "Once the company got onto the internet" doesn't make sense by itself, but it helps to form the whole sentence. Also, "The Dale and Thomas Popcorn Company quadrupled its business" makes sense by itself.

Main idea on left, details on right