《煤矿安全规程》规定2台局部通风机供风时，2台局部通风机都必须同时采取什么安全措施？
参考答案：
必须同时实现风电闭锁。
The famous professor’s lectures, though ____ informal, are considered far more informative and interesting.
A．occasionally
B．constantly
C．regularly
D．usually
_______ the Internet is of great help, I don't think it's a good idea to spend too much time on it.
A If B While C Because D As
