In most western countries, on April Fool’s Day, people often play        trick on each other; children especially have great        fun.

A．a; a

B．the; the

C．a; /

D．/; a

下列说法正确的是 (　　)。

A．所有不锈钢都只含有金属元素

B．我国流通的硬币材质是金属单质

C．广东打捞的明代沉船上存在大量铝制餐具

D．镁合金的硬度和强度均高于纯镁