Plastids that are surrounded by more than two membranes are evidence of
a. evolution from mitochondria.
b. fusion of plastids.
c. origin of the plastids from archaea.
d. secondary endosymbiosis.

d. secondary endosymbiosis.

Explanation:

When a living cell acquires another organism that eventually becomes a part of this cell, this process is known as primary endosymbiosis.When an organism that has already undergone primary endosymbiosis engulfs another eukaryotic organism then this process is known as secondary endosymbiosis. Secondary endosymbiosis has been known to occur in plastids because of which they are surrounded by two membranes. This bilayer is present because one of the layers is the original outer membrane of the organism and the other membrane is that of the organism that has been engulfed.

The correct answer is  b)