How Is Pollen Tube Elongation Facilitated

How is pollen tube elongation facilitated?

A) Pollen tube growth relies on chemical signals released by the pollen grain.
B) Pollen tube elongation will occur as long as the pistil provides moisture and energy.
C) Chemical cues from female tissues help guide pollen tube growth, but the identity of these chemicals is not known.
D) All the details of the chemical interactions between the pollen tube and pistil tissue have been elucidated and are well-described.
E) Pollen tube elongation occurs only in the absence of chemical cues from the female tissues.