若数据2，3，-1，7，x的平均数为2，则x=______．
由题意得，15（2+3-1+7+x）=2，
解得：x=-1．
故答案为：-1．
公益性投资项目不实行( )。
A．项目法人责任制
B．资本金制度
C．招投标制度
D．工程建设监理制度
---- Did he give you advice on your work yesterday?
---- Yes. But his advice, as a matter of fact, ______ my difficulty.
A．used to
B．related to
C．added to
D．belonged to
