阅读理解。 Our boat floated on, between walls of forest which were too thick to allow us a view of the land we were passing through, although we knew from the map that our river must from time to time be passing through chains of hills which crossed the jungle plains. Nowhere did we find a place where we could have landed: where the jungle did not actually spread down into the river, banks of soft mud prevented us going ashore. In any case, what would we have gained by landing? The country was full of snakes and other dangerous creatures and the jungle was so thick that one would be able to advance only slowly, cutting one's way with knives the whole way. So we stayed in the boat, hoping that when we reached the sea, a friendly fisherman would pick us up and take us to civilization. We lived on fish, any fruit and nuts we could pick up out of the water. As we had no fire, we had to eat everything, including the fish, raw. I had never tasted raw fish before, and I must say I did not much enjoy the experience: perhaps sea-fish which don't live in the mud are less tasteless. After eating my fish, I lay back and dreamed of such things as fried chicken and rice, and ice cream. In the never-ending heat of the jungle, ice cream was a particularly frequent dream. As for water, there was a choice. We could drink the muddy river water, or die of thirst. We drank the water. Men who have just escaped what had appeared to certain death lose all worries about such small things as diseases caused by dirty water. In fact, none of us suffered from any illness as a result. One day we passed another village, but fortunately nobody saw us. We did not wish to risk being taken prisoners a second time: we might not be so lucky as to escape in a stolen boat again. 1. The only thing that they could see in the boat was _______. A. chains of hills B. high walls C. vast land D. tall trees 2. They were prevented from landing because they could not _______. A. find the place marked on the map B. go through the thick forest C. go across the soft mud D. see the plains 3. This passage is mainly about ______. A. the problem of landing B. a terrible experience C. walls of forest D. the fishermen's worries 4. Which of the following is NOT true according to the passage? A. The author and his partners were trapped during scientific exploration. B. They were floating on a small boat in the jungle without help. C. The dirty water they drank didn't threaten their lives. D. They had no food or drinking water prepared.