依据不同的分类标准，定金合同属于（）。
A.双务合同
B.单务合同
C.诺成合同
D.实践合同
E.从合同
参考答案：A, D, E
China develops rapidly in economy，especially in space， draws many western countries’attention．
A．which
B．what
C．it
D．that
______ environmental damage is done, it takes many years for the ecosystem to recover.
A．Even if
B．If only
C．While
D．Once
