世界上最长的山脉是（　　）

    My name is Sam. This September I am going to middle school. I am going to London Middle School. I am really excited. The school is near my house. I am going to school on foot. I am going to study History, Science, Geography and French. I'm also going to speak Chinese there.

下列哪一项不是哺乳动物的主要特征？（  ）

为了考察两个变量x和y之间的线性相关性，甲、乙两个同学各自独立地作10次和15次试验，并且利用线性回归方法，求得回归直线分别为l₁和l₂．已知在两个人的试验中发现对变量x的观测数据的平均值恰好相等，都为s，对变量y的观测数据的平均值也恰好相等，都为t．那么下列说法正确的是（　　）