单项选择题
A．He walked a long distance. B．He is tired. C．He’s wet. D．He lost his raincoat.
A．How are Cloud Droplets Formed B．How is Rain Formed C．Cloud Droplets and Water Droplets D．How are Ice Crystals Produced
A．we can pin down the exact value of the universe’s age B．we can work out the universe’s size C．we still can’t know the exact age of the universe D．we can more reliably solve the broader picture of the universe’s origin, evolution, and destiny