The world’s population is getting larger and larger, so scientists are trying to _______ new ways to solve the food problem.

—Does Hong Kong Disneyland ________different parks?—Yes, there are four parks in it, ________Tomorrowland and Fantasyland.

Rather than _________ on a crowded bus, he always prefers __________ a bicycle.

 —The river smells so terrible! How did it come about?—People used to pour dirty water into it.

 All lights______after the students left the classroom.