_____ of the twins has been there before.
—Have you brought with you? We won’t have time to come back.—Don’t worry. All the things we need are here, in this big bag.
The World Expo (世博会) ____________ in Shanghai now.
Beijing, the capital of China, is one of __________ cities in the world.
How time flies! Three years ____________ really a short time.
I felt it hard to keep up with my classmates. But whenever I want to ____________, my teacher always encourages me to work harder.