-- are the Olympic Games held? --Every four years.
Mary was born in 1998 and she began to play ________ guitar at the age of seven.A.aB.不填C.the
—Can you play foot ball?—________.It’s hard.
In some Western countries shops are closed ________ weekends.
Our teacher always helps us ________ our English.
The desk is not dirty.You ________ clean it.