完形填空
During a trip to observe wild animals in Africa, I encountered the least brave animal on earth, the wildebeest (角马). I sat on a riverbank for three hours watching a group of thousands build 【C1】______the courage to drink water. More than a million wildebeests【C2】______northward into the wetlands. It is a long, dry and difficult journey. Frequently, the only available water is the Grumeti River, 【C3】______represents both life and death. Unlike some creatures that can take moisture【C4】______the grass they eat, wildebeests must drink from the river to live. The river supports other wildlife, including【C5】______that kill and eat other animals. Though thirsty【C6】______traveling, the wildebeests stand back from the water, sensing possible danger. Moving slowly toward the bank can【C7】______hours, as an individual wildebeest steps forward, steps back and then carefully steps forward again. More wildebeests gather together and advance, gradually pushing the leaders to the river, 【C8】______they want to go or not. It' s been a long time【C9】______they drink last time, and you feel their anxiety for water. Lions are possibly on the【C10】______, saving energy as they wait for an opportunity for lunch. Once the large group moves to the river, lions could【C11】______, making the group running in a wild and uncontrolled【C12】______. The mad rush would raise a dust cloud that blocks the【C13】______of the wildebeests nearby. A kill is almost guaranteed. Sitting on that riverbank, I noticed that a young wildebeest finally stepped ahead and drank while the【C14】______adults held back. Soon, others began drinking. But【C15】______lining up along the bank, taking turns, they gathered and pushed. Some had to walk farther into the water than they were【C16】______to go. Those pushed farther in water got frightened and in【C17】______frightened the others. They all retreated hastily and returned to their route. Only the few that were【C18】______enough got a drink. The others went【C19】______. There was no danger that day. Only the wildebeests' fear and【C20】______of courage kept them from drinking.