The world’s population is getting larger and larger, so scientists will have to ______ new ways to solve food problem.
—How often do I need to feed the dog? —It ________ food every day, or it will be hungry.
—It's difficult to get to the other side of the river. —I think a bridge ________ over the river.
Flowers_____ along the road last year.
.Pens are used for on paper.
— Do you know in ancient China? — I have no idea. But I know people once used tree leaves to make paper.