A. Ann wants to be a nurse. She wants to look after sick people (照顾病人). B. Mrs Green is a taxi driver. She likes driving. She is good at driving. C. Jerry wants to be a fireman. He is not afraid of fire. He wants to fight fires. D. This is Jim. He wants to be a policeman (警察).He wants to help people. | 
与任何向量不能构成空间向量的一组基底，那么
为空间四点，且向量
不构成空间的一个基底，则点
是空间的一个基底，则向量
也是空间的一个基底。