Mary was born in 1998 and she began to play _______ guitar at the age of seven.A.a B.不填 C.the
Great changesin China in the past 20 years.
We will have a _____ holiday after the exam .
Though it was late , _____ he went on with his work .
We ____ here two hours ago . We____ here for two hours .
He has a friend who ____ the piano very well .