单选题 ______ no conclusive evidence exists, many experts believe that the wheel was invented only once and then diffused to the rest of the world.

A、 Even
B、 But
C、 Although
D、 So

【正确答案】 C

【答案解析】although具有“虽然，尽管”的意思，常用来引导让步状语从句。该词引导的从句包含着阻碍主句行为或状态发生的不利条件，如：Although(Though)malice may darken truth，it cannot put it out．恶意可以污蔑真理，却不能抹煞真理。