What is Don Quixote's motivation for fighting the giants?

Part I, Chapter 7 says:

Just then they
came in sight of thirty or forty windmills that rise from that plain. And no sooner did
Don Quixote see them that he said to his squire, "Fortune is guiding our affairs better
than we ourselves could have wished. Do you see over yonder, friend Sancho, thirty or
forty hulking giants? I intend to do battle with them and slay them. With their spoils
we shall begin to be rich for this is a righteous war and the removal of so foul a brood
rom off the face of the earth is a service God will bless."

"What
giants?" asked Sancho Panza.

"Those you see over there,"
replied his master, "with their long arms. Some of them have arms well nigh two leagues
in length."

"Take care, sir," cried Sancho. "Those over
there are not giants but windmills. Those things that seem to be their arms are sails
which, when they are whirled around by the wind, turn the
millstone."

—Part 1, Chapter VIII
Therefore,
the answer is C) BOTH A AND B
Remember also that Don Quixote was so anxious of
fighting that anytyhing was tempting to him. Therefore, it is not strange at all that he
should voluntarily confuse windmills with giants.