阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项，并在答题卡上将该选项标号涂黑。
A
The very next day we did actually make our start upon this remarkable expedition (探险). At dawn and at sunset, the monkeys screamed together and the parrots started making their high-pitched (声调高的) noise, but during the hot hours of the day only the loud noise of insects, like the beat of a distant surf, filled the ear, while nothing moved amongst the views of huge tree trunks, fading away into the darkness which held us in. Once some creature, an anteater（食蚁兽）or a bear, walked awkwardly amid the shadows. It was the only sign of life which I had seen in this great Amazonian forest.
And yet there were signs that even human life itself was not far from us in those mysterious dark corners. On the third day out we were aware of a strange, deep, rhythmic beat in the air, coming and going on and off throughout the morning. The two boats were moving within a few yards of each other when first we heard it, and our guides remained still, as if they had been turned to bronze.
“What is it, then?” I asked.
“War drums,” said Gomez. “Native people, aggressive, not friendly; they watch us every mile of the way; kill us if they can.”
“How can they watch us?” I asked, gazing into the dark.
“The native people know. They talk the drum talk to each other. Kill us if they can.”
By the afternoon of that day—my pocket diary shows me that it was Tuesday, August 18th—at least six or seven drums were beating from various points. Sometimes they beat quickly, sometimes slowly, sometimes in obvious question and answer, one far to the east breaking out in a high-pitched beat, and being followed after a pause by a deep roll from the north. There was something incredibly nerve-shaking and threatening in that constant noise, which seemed to shape itself into the words: “We will kill you if we can.” No one ever moved in the silent woods.
That night we tied our boats with heavy stones for anchors (锚) in the centre of the stream, and made every preparation for a possible attack. Nothing came, however, and with the dawn we pushed upon our way, the drum-beating dying out behind us.
21. What does the author intend to do in paragraph 1?
A. Show his preference for nature.
B. Create an atmosphere of mystery.
C. Emphasize the importance of the expedition.
D. Admire the splendid scenery in Amazonian forest
22. How did the guides feel when the drums started?
A. Curious. B. Confused. C. Relieved. D. Scared.
23. Why did the natives change the speed of the drums?
A. To practice their drum skills. B. To interact with each other.
C. To attract the visitors in the forest. D. To frighten off the dangerous animals.
