A difference between primary and secondary endosymbiosis is that A. the descendants of primary endosymbionts were nonphotosynthetic B. secondary endosymbiosis involves ingestion of a bacterium by a eukaryotic cell. C. cells resulting from secondary endosymbiosis may have plastids surrounded by four membranes D. secondary endosymbiosis takes place only in prokaryotes.

Option-C

Explanation:

Endosymbiosis theory explains that a eukaryotic organism evolved when the proto-eukaryote engulfed the prokaryotes.  The endosymbiosis took place in three to four phase: primary, secondary, tertiary.

Primary endosymbiosis of plastid occurred when the proto-eukaryotes engulfed the cyanobacterium and the resultant cell became photosynthetic. This engulf added the second layer to the plastids.

Secondary endosymbiosis occurred when the primary photosynthetic eukaryotes were engulfed by another eukaryote and added further lipid layers and the organelles could have four membranes.

Thus, Option-C is the correct answer.