One of the most important problems we will have to solve is ____of students’ learning method.
____ is known to all is ____ Diaoyu Island is part of China.
----Where does your father work, Lucy? ----In England. But he _____ in France for 8 years.
It is many years ____ we enjoyed ourselves on the great occasion.
Three of the town’s factories have closed down _____ the space of a year.
Not having promoted the new digital camera successfully, the company should its original marketing methods.