The population problem may be ______ one of the world today.
The students in our school have ________ days off and spend _________ time doing their homework.
When it grows ________, it will grow ________ a strong animal.
—________ does John go to school? —He takes the underground.
Mr Wu is one of ________ in our school.
I don’t like eggs ________ milk, ________ I like fish ________ meat.