As more and more cars are produced and used, so the _____ from their exhaust-pipes contains an even larger volume of poisonous gas.
. We looked forward, only ________ a narrow path ______ to the top of the mountain.
Jane is looking forward to _____ from me. Remember ______ my letter on your way home.
______ the call for help, the boys immediately rushed out to see what was going on.
______ their life in the past, ours is much better.
The soldiers ran as fast as they could, ______ to catch the fleeing enemies.