What Flower Mechanism(s)would NOT Help Prevent Pollination by a Foreign

What flower mechanism(s) would NOT help prevent pollination by a foreign species?

A) A pollen tube only grows in the style of its own species.
B) The stigma is sticky mainly to its own species of pollen.
C) The timing of flowering varies by species and keeps pollinators moving among a limited number of species.
D) Flowers attract a small number of specialized pollinators, and therefore pollen is not spread equally to all available species of flowers.
E) Flowers of different species are the same color and attract similar pollinators.