题目

完形填空阅读下面短文，掌握其大意，然后从各题所给的四个选项中，选出一个最佳选项。Food is important. Everyone needs to   1   well if he or she wants to have a strong body. Our minds also need a kind of food. This kind of food is  2  . We begin to get knowledge (知识) even when we are young. Small children are   3   in everything around them. They learn  4  while they are watching and listening. When they are getting older they begin to    5 story books, science books and anything else they like. When they find something new, they have to a已知向量．    （1）若△为直角三角形，求值；    （2）若△为等腰直角三角形，求值