单选题 The only thing ______ really matters to the parents is how soon their children can return home.
A. what B. that C. which D. this

【正确答案】 B

【答案解析】本题考查定语从句的连接词问题，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，关系代词常用出at，不用which，who或whom。