根据句子意思，用所给单词的适当形式填空。未提供单词的根据上下文填入适当的词。 A river ran down from a mountain through many villages and forests. Then it　 　 (arrive) at a desert. "I went through so many 　 　 (problem). I should have no trouble crossing the desert, she thought. As she started, she found herself disappearing　 　 (slow) into the sand. After many tries, she still failed.　 　this time, a deep voice said, "If a breeze(微风) can cross the desert, so can a river." It was　 　voice of the desert. But the river answered, "That's because a breeze can fly, but I can't.""That's because you can't give up　 　 you are. Let yourself evaporate(蒸发)into the breeze and you can cross the desert easily," said the desert."Give up what I am now? No! No!" the river　 　 (agree)with this idea." The breeze can carry the vapour 　 　 (cross) the desert and let it leave as rain. The rain will form a river again, "said the desert. "And whether you're a river or vapour, your nature(本性) never changes.After 　 　(hear) this, the river didn't feel 　 　. (frighten). It went into the open arms of the breeze. It carried her to the next stage of her life.