多项选择题
A.< asp：Button ID="btn"runat="server"click="btn_Click"/>
B.< asp：Button ID="btn"runat="server"onclick="btn_Click"/>
C.< asp：Button ID="btn"runat="server"onclientclick="btn_Click"/>
D.private void btn_Click（object Sender，EventArgs e）{...}
E.protected void btn_Click（object Sender，EventArgs e）{...}