[A,B,C & D] Are Stimuli Laid Out Left to Right

Multiple Choice

[A,B,C & D] are stimuli laid out left to right, [1,2,3,4] are responses laid out left to right. Which mapping will have the longest average RT?

A) A1 B2 C3 D4
B) A2 B3 C4 D1
C) A4 B3 C2 D1
D) both b and c above