Chloroplasts of certain algal taxa such as Cryptophyta are surrounded by fourmembrane envelope. The most likely reason for the origin of four-membrane enveloped chloroplast structure is _____ .

• Correct answer
  A

  secondary endosymbiosis, where a photosynthetic eukaryote was engulfed by another eukaryote.
• B

  engulfment of the acquired chloroplast by host endoplasmic reticulum during the course of evolution.
• C

  fusion of the acquired chloroplast with host membrane vesicles during the course of evolution
• D

  acquisition of new genes to synthesize an additional membrane envelope around the acquired chloroplast

Hence, the correct answer is option: 'A'.