B、reached
因为都是reach 就只有时态是问题.
主句如下:The letter ——me .所以要添谓语动词,A不对,因为是过去时态.
所以CD都不行.
这个:three days later than I had expected.后置的状语.
I had been looking forward to 是letter的定语从句,都不影响.