During biological evolution, the first living organisms were _______AAutotrophsBHeterotrophsCEukaryotesDProkaryotic plantsAnswer: B. Heterotrophs Read Explanation: Heterotrophs were first living organisms to evolve, as they originated among organic molecules and oxygen-free atmosphere. They were anaerobes capable of respiration in the absence of oxygen.They only depended on the existing molecule for their nutrition. Read more in App