4. which of the following factors did not contribute to the genetic diversification of the galápagos island finches studied by darwin?
a. environmental conditions vary among the different islands.
b. most of the islands are sufficiently distant from one another such that movement among their populations is limited.
c. the islands are only 100 km from ecuador, so they receive a continual input of new genes from the mainland.
d. occasional migrants to new islands rarely interbreed with endemic species.
e. over time, the residents of each island have developed their own genetic distinctiveness.

c. The islands are only 100 km from Ecuador, so they receive a continual input of new genes from the mainland

Explanation:

The Galapagos islands are not connected with the mainland. They are isolated islands and are located away from the mainland. Due to their geographical isolation, Galapagos islands do not experience the migration of populations from the mainland. So, there is no gene flow to Galapagos islands from the mainland.

Further, diversification of islands needs them to be isolated from the mainland so that the inhabiting populations can diversify to accommodate in available niches.  

"a.) well–developed vascular system."

the answer would be..

b. sucking