人字缝
参考答案：
指两块顶骨与枕骨交界处的骨缝。
—Sorry, I can't work out this problem.
—Try again, please.It's only _____ difficult. [ ]
A. a bit
B. a lot
C. a bit of
D. much too
能提高肌肉组织兴奋性，对横纹肌有良好的刺激收缩作用的电针波型为( )
A．密波B．疏波C．断续波D．连续波
