【单选题】

Which of the following is true about the author's attitude towards "litmus test" in America
A．(A) The effectiveness of litmus test is greatly undermined by its failure to judge politicians on a variety of positions.

B．(B) It's unfair to exclude a politician who fails a certain litmus test from the presidency.
C．(C) Current litmus tests like abortion or gun control are not reliable indicators of public opinions.
D．(D) Some specific litmus tests on certain issues axe fundamental in shaping people' s judgment of politicians.