语法与词汇 The only thing ______really matters to the parents is how soon their children can return home.
【正确答案】 B
【答案解析】本题考查定语从句的连接词的问题，如果先行词被形容词最高级或first，last，any，only，few，mush，no，some，very等词修饰，关系代词常用that，不用which，who或whom。