※ 引述《truthlier》之銘言：
: A. has been established by carbon dating, but what is much more difficult to
: determine are
: B. have been established by carbon dating, but what is much more difficult to
: determine are
: C. have been established by carbon dating, but that which is much more
: difficult to determine is
: D. has been established by carbon dating, but what is much more difficult to
: determine is
: E. are established by carbon dating, but that which is much more difficult to
: determine is
: 答案是D
: 對於A有疑惑，因為後面接的是the use..., the reason..., and the meaning of...
: 想請問一下A選項中的are為何錯?
what=the thing that，基本上what是單數或複數要看be動詞後面的名詞，在AD選項
都是已經說what is more difficult已經告訴你the thing是單數，所以當然動詞配單數
