在常温下，将下列物质投入足量稀盐酸中，能产生气体且有金属不溶物残留的是[ ]
A.黄铜
B.纯铁
C.碳酸钙
D.碳素钢
答案：A
They said that they ______ a wonderful time in Beijing and they hoped to be there again.
A．had
B．would have
C．would have had
D．could have
对（）由民政部门设立的儿童福利机构收留抚养。
A.孤儿
B.无法查明其父母或无法查明其他监护人
C.其他生活无着落的未成年人
D.留守儿童
