若关于x的方程2x2+4x+k=0有两个相等的实数根，则k的值是（ ）。
2
.--I sent him a most interesting story book by mail this morning.
--You____so; he's coming tomorrow morning.
A．needn't do
B．needn't have done
C．don't need to do
D．didn't need do
联合国工业发展组织从资金投入—产出循环的角度，将项目周期划分为( )时期。
A．6个 B．5个C．4个D．3个
