对质量守恒定律的解释正确的是（　　）

A．化学反应前后，分子的数目不变，原子的数目不变

B．化学反应前后，原子的种类不变，原子的数目改变

C．化学反应前后，原子的数目不变，原子的种类改变

D．化学反应前后，原子的种类、数目、质量都不改变

When all the people had assembled, the king, surrounded by his court, (21) a signal. Then a door beneath him opened, and the accused man stepped (22) into the arena. Directly opposite him were two doors, exactly (23) and side by side. It was the duty and the privilege of the (24) on trial to walk directly to these (25) and open one of them. He (26) open either door he pleased; he was subject to no (27) or influence. If he opened the one, there came out of it a hungry tiger, the (28) and most cruel that could be found, which (29) sprang upon him and tore him to pieces as a punishment for his guilt. (30) , if the accused person opened the other door, out of it came a (31) lady, and to this lady he was immediately married, as a reward of his innocence. This was the (32) method of administering justice. Its perfect fairness is obvious. The criminal could (33) know out of which door would come the lady; he opened either he pleased, without having the slightest (34) whether, in the next instant, he was to be devoured or married. So the accused person was instantly (35) if guilty, and, if innocent, he was rewarded on the spot.

31（）

A．little

B．angry

C．beautiful

D．old