The development of industry has been ____ gradual process throughout ______human existence, from stone tools to modern technology.
You _____be careful with the camera. It costs!
Jane’s grandmother had wanted to write children’s book for many years, but one thing or another always got in way.
——Hi, John. Are you busy?——
Yang Liwei showed the flags of China and the United Nations, ________ the wishes of Chinese people to use space peacefully.
-- The last one ________ pays the meal. --- Agreed.