A child has type O blood. Which of the following couples could be the child's parents?
Couple Mother's Type Father's Type
1 A - B
2 O - A
3 AB - O
4 B - AB
A. couple 1 or 2 only
B. couple 3 or 4 only
C. couple 2, 3, or 4 only
D. couple 1, 2, 3, or 4