Choose the closest paraphrased version after each of the followi

Choose the closest paraphrased version after each of the following sentences or the italicized part.
It is rather the most disturbing element in civilization, the most profoundly revolutionary thing which has ever been let loose in the world.
A、the revolution that human race is not ready to welcome.
B、the greatest challenge that mankind has ever had to meet.
C、the unexpected thing that takes some time for people to accept.
D、the new inventions that people in the modem world are facing.
【正确答案】：B