闪光焊和气压焊缝探头频率应选用（）。
参考答案：≥4MHz
You can always _____ a dictionary if you meet new words during your English study. [ ]
A. set up
B. come to
C. turn to
D. get to
脑膜瘤来源于
A．硬脑膜外层B．硬脑膜内层C．蛛网膜D．硬脑膜E．软脑膜
