Riley Has an AB⁺ blood Type

Riley has an AB⁺ blood type. He is worried about the baby that his wife, Lena, is carrying. When should Riley be worried?

A) If Lena has a negative blood type.
B) If Lena has an O blood type, regardless of whether it is positive or negative.
C) If Lena has an A⁺ blood type.
D) If Lena has a B⁺ blood type.