题目

下列说法正确的是（） A . 对角线相等且互相垂直的四边形是菱形 B . 对角线互相垂直的梯形是等腰梯形 C . 对角线互相垂直的四边形是平行四边形 D . 对角线相等且互相平分的四边形是矩形 答案：D By serving others, a person focuses on someone other than himself or herself, __________ can be very eye-opening and rewarding. A. who    B. which C. what   D. that