Dropping litter ______ never allowed in our city.

Those who _________ singing may join us.

—Each boy and each girl     talking about optional courses（选修课）.—Yes! And the each     their favorite one!

Neither the children nor the teacher________.

—He is the only one of the students ______from the country in my class, and we have known for quite some time.—Where did you meet for the first time?     —It was on the farm ________ I used to work.