我国戈壁大沙漠中植物稀少,起决定作用的非生物因素是
He was about to leave the office for home _______someone knocked the door and asked for some help.
If you find yourself ______ no one will help you, please call me.
The government has taken some measures to solve the shortage of water, but it may be some time __ the situation improves.
— Why was it so noisy over there?— The Twins were surrounded by their fans ____ they stepped out of the hall.
Among the many dangers_________-- sailors have to face, probably the greatest of all is fog.