Morgan observed a higher number of recombinant offspring involving eye color and wing length (401 + 318) than those involving body color and eye color (17 + 12). These results occurred because

a. the genes affecting eye color and wing length are farther apart on the X chromosome than are the genes affecting body color and eye color.

b. the genes affecting eye color and wing length are closer together on the X chromosome than are the genes affecting body color and eye color.

c. the gene affecting wing length is not on the X chromosome.

d. the gene affecting body color is not on the X chromosome.