For summary questions we must learn to pick the broader keywords and connect them together to form the summary. In this paragraph the author uses two broad keywords "genetic theory and metabolic theory. The genetic theory was successful because of the diversity of genetic models, and the same might happen for metabolic theory, which would provide a conceptual foundation for much of ecology." The contrast in choice 2 makes the choice an incorrect one because the author stresses on similarity, not contrasts. Option 1 says "metabolic theory must have the wide range of theoretical models". The word "must" makes this choice an incorrect one. The author talks about a possibility, not a necessity. Option 4 goes out it because it misses discussing the keyword "metabolic theory" and how it is compared with genetic theory. 3 is the right choice.