Answer: C) GMOs, genetically modified foods engineered in a lab to produce desirable traits.
Explanation:
The genetic engineering involves the insertion of genes from other organism to the host organism so as to make up genetically modified organism. Some unwanted and default genes are also removed from the organisms so that their body function properly. 
The genetically modified foods are the examples of genetic engineering. This is done to produce desirable traits in the food crops. In plants both plants and animal genes are inserted to improve the yield of crops, and to improve their quality. In animals, the insertion of genes of other animals is likely to improve the milk and meat yield. 
 
        
             
        
        
        
By acting as decomposers on dead plants and animal
        
                    
             
        
        
        
I think the correct answer from the choices listed above is option B. You can find methanogens in the human intestines. These organisms can  work with or without oxygen. Too much of oxygen for them is toxic. They are obligate anaerobes.
        
             
        
        
        
The question is incomplete. The complete question is:
Question: Why do organisms without oxygen need to convert pyruvate to lactate?
A) because pyruvate is toxic to the cells
B) in order to regenerate NAD+
C) in order to use lactate in the citric acid cycle
D) because lactate is needed to produce ATP
Answer:
B) in order to regenerate NAD+
Explanation:
Kreb's cycle and electron transport chain (ETC) are the aerobic stages of cellular respiration. ETC regenerates NAD+ and FAD+ by oxidation of NADH and FADH2 produced during glycolysis and Kreb's cycle. Here, oxygen serves as the terminal electron acceptor. 
Glycolytic reactions use NAD+ as an electron acceptor and produce NADH. Therefore, a constant supply of NAD+ is required to sustain glycolysis. In absence of oxygen, ETC cannot occur and organisms convert pyruvate into lactate. Pyruvate is reduced in lactate and NADH serves as the electron donor. Thereby, lactate fermentation regenerates NAD+ to continue the process of glycolysis. 
 
        
             
        
        
        
Answer:
2) B
3) D
I believe that these are the answers, I hope this helps!