问题
选择题
Stop! You can never touch this machine when it ________, it is very dangerous.
A．has been operated
B．will be operated
C．is operated
D．is being operated
答案
答案：D
考查时态及语态。句意：停止，你根本不能触摸这台机器当它正在被操作的时候，它非常的危险。根据语义机器被操作的时候应用现在进行时的被动语态。故选D。