题目

设集合，，且，求实数的取值范围． 答案：，分为两种情况： ①当时，满足，此时，解得 ②当时，有，解得 综上所述，可得的取值范围是– Do you know what has happened in Japan recently?       -- The earthquake! It’s _____ one that I have ever heard of.      A. a very serious          B. a more serious         C. the most serious