The Expo park should be ______ from anywhere in the city of Shanghai within 90 minutes by bus, subways and special taxis.
—What about ____ book? —It’s too difficult ____ book for beginners.
Whenever you are in trouble ,don’t hesitate _____us for help.
It was the longest film we have ever seen ; it ____ three hours..
___ was invented by Grain Bell..
We must ___ on our study..