Choose the best topic sentence from the four options below.

Choose the best topic sentence from the four options below.

A.Nuclear power plants cost a lot of money to build and to operate.

B.Nuclear power has been proven to be an uneconomical energy source.

C.Nuclear fuels must be mined, refined, and transported over great distances.

D.There are no nuclear power plants in such African countries as Ethiopia and Rwanda.

正确答案是B