题干
They're trying their best to enough money to build a school for the poor children.
A：spend
B：cost
C：collect
D：pay
答案(点此获取答案解析）
C
They're trying their best to enough money to build a school for the poor children.
A：spend
B：cost
C：collect
D：pay
”“ 
”分别表示氢、氯、氧三种不同元素的原子，其中表示单质的是（ ）