完形填空, 阅读下面短文，掌握其大意，然后在每小题所给出的A、 B、 C三个选项中选出最佳选项，
It was a long hard fight, but by now it was 1and this helped us very much. We ran here and there in the trees, calling and2. The enemies could not see us and did not know how many of us they were 3In the end the first officer shouted to them：
“Put down your4and stop fighting! The captain has fifty island people to help him. We can kill you 5!”
So the enemies 6 fighting and we took their guns. Three of the enemies7 to come to join us, but the others refused. So we 8them in my cave. I stayed to 9 the prisoners(犯人), while the captain and his men went back to fight for the ship.
All night we listened to the 10of guns and shouting, but in the morning, when the sun 11, the captain was master of his ship again. I went down the shore(海岸) to meet him.
“My dear friend” he cried, “There's your12! I’ll take you to the ends of the13in it!” I put my 14round him, and we laughed and cried together. How 15I was to leave the island.
4NO + 6H2O，则X的化学式为（ ） 