What observation led researchers to propose that chloroplasts evolved from cyanobacteria? a) both produce proteins. b) both contain mitochondria. c) both provide structure to cells. d) both perform photosynthesis.

(D) Both perform photosynthesis is the observation that led researchers to propose that chloroplasts evolved from cyanobacteria.
Chloroplasts is the area where photosynthesis takes place. It is a green organelle in a plant cell. Pigments called the chloros in a chlorophyll are needed for the photosynthesis.
Cyanobacteria or blue-gree algae contains a blue photosynthetic pigment and a chlorophyll for photosynthesis.