21. The development of industry has been _____ gradual process throughout _____ human existence from stone tools to modern technology.
A. 不填；the B. the；a C. a；不填 D. a；a
22. — Sorry I’m late. I got stuck in traffic.
— _________. You’re here now. Come in and sit down.
A. You are welcome B. That’s right C. I have no idea D. Never mind
