When Pollen from One Species Lands on the Stigma of a Flower

When pollen from one species lands on the stigma of a flower from another species, the pollen tube typically ____.

A) does not develop
B) forms, but the sperm cannot penetrate the egg
C) forms and grows to the ovary, but then stops
D) forms, but the sperm are killed
E) forms and the egg is usually fertilized, but the embryo rarely grows