足月妊娠时，羊水无回声区最大前后径为（）
A.10cm
B.2cm
C.4cm
D.5cm
E.6cm
参考答案：E
等边三角形绕它的中心至少旋转______度，才能和原图形重合．
To ensure the project team provides the functionality the customer expects in a new piece of software, the project manager asks the customer for sign-off on the design criteria. These documents are ______ .
A．technical specifications
B．performance specifications
C．product descriptions
D．quality assurance
