闸阀具有制造较截止阀复杂，密封面磨损后不易维修的缺点。
参考答案：对
I’ve ____ met her before, so I don’t know her.
A．never
B．ever
C．just
D．yet
下列哪些不属于颈浅丛属支()
A．lesser occipital nerve
B．great auricular nerve
C．transverse nerve of nerve
D．supraclavicular nerve
E．trochlear nerve
