A travel company wants to charter a plane to the Bahamas. Chartering the plane costs $8,000. So far, 18 people have signed up for the trip. If the company charges $300 per ticket, how many more passengers must sign up for the trip before the company can make any profit on the charter ？（）

A. 7

B. 9

C. 13

D. 27

E. 45

什么是计划生育的“两个转变”？