How Did Heterospory Facilitate the Colonisation of Drier Environments

How did heterospory facilitate the colonisation of drier environments?

A) It facilitated the development of more environmentally resilient microspores.
B) It resulted in a single spore with a rigid cell wall that could survive ingestion.
C) Gametangia and megasporogenesis no longer required water for functionality.
D) It overcame the previous requirement for water to disperse pollen.
E) Microsporangia shrunk to a size that facilitated wind dispersal.