题干
—Are these your brother's books?
—Yes, ______are.
A：this
B：that
C：these
D：they
答案(点此获取答案解析）
D
—Are these your brother's books?
—Yes, ______are.
A：this
B：that
C：these
D：they
仅在封闭区域
内（包括边界）的点
处取得最大值，则
的取值范围是 （ ）