紧急请教GMAT数学题

bosfashion

the rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present. If the chemical B is increased by 100 persent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A. 100% decrease

B. 50% decrease

C. 40% decrease

D. 40% increase

E. 50% increase

答案是第四个，我不明白。请各位讲的详细一些！谢谢了