Suppose "A" is a dominant gene for the ability to taste phenylthiocarbamide and "a" is a recessive gene for inability to taste it. Which of the following couples could possibly have both a child who tastes it and a child who does not?

    *a.    father Aa, mother AA
    b.    father Aa, mother AA
    c.    father AA, mother AA
    d.    father AA, mother aA