Everyone may not know what breaking in is, therefore I will describe it. It means to teach a horse to wear a saddle and bridle, and to carry on his back a man, woman or child; to go just the way they wish, and to go quietly. Besides this he must learn to wear a collar, a crupper, and a breeching, and to stand still while they are put on; then to have a cart fixed behind, he cannot walk or trot without dragging it after him; and he must go fast or slow, just as his driver wishes. He must never start at what he sees, nor speak to other horses, not bite, nor kick, nor have any will of his own, but always do his master's will, even though he may be very tired or hungry; but the worst of all is, when his harness is once on, he may neither jump for joy nor lie down for weariness. This breaking in is a great challenge. I had of course been used to a halter and a headstall, and to be led about in the fields and lanes quietly, but now I was to have a bit and bridle; my master gave me some oats as usual, and after a good deal of coaxing he got the bit into my mouth, and the bridle fixed. Those who have never had a bit in their mouths cannot think how bad it feels; a great piece of cold hard steel as thick as a man's finger to be pushed into one's mouth, between one's teeth, and over one's tongue, with the ends coming out at the corner of your mouth, and held fast there by straps over your head, under your throat, round your nose, and under your chin; so that no way in the world can you get rid of the nasty hard thing; it is very bad!

Which one of Black Beauty’s thoughts contributes to the theme of the story?
A.
"my master gave me some oats as usual"
B.
"no way in the world can you get rid of the nasty hard thing"
C.
"he must never start at what he sees"
D.
"he may neither jump for joy nor lie down for weariness"