Look!The students __(show)how to operate the machine by the engineer.
问题描述：
Look!The students __(show)how to operate the machine by the engineer.
答
are being shown（现在进行时的被动语态）、
看!工程师正在向学生们展示如何操作机器.
注意后面的by the engineer,是被动语态,同时look暗示了用现在进行时态.