单项选择题
We have just received a message from shore（）assistance is on the way.
A.When B.Where C.how D.that
单项选择题 （）we stand away from the church bell, it takes time for the sound waves to reach us.
单项选择题 Before（）, a station shall take precautions to ensure that its emission will not interfere with transmission already in progress.
单项选择题 Two vessels（）while they re sailing in Huangpu River.
