Correct about ectotherm and endotherm efficiency:
The keyed combination is A and C, yet the underlying assertions A–D are missing. In general, ectotherms spend relatively little assimilated energy maintaining a constant high body temperature and often show greater production efficiency than endotherms. Endotherms have high respiratory costs for thermoregulation, although assimilation efficiency also depends strongly on food quality and digestive physiology. These accepted principles support comparison of efficiencies, but they cannot establish which absent lettered statements correspond to them. Reliable inference requires the complete experimental design, definitions, units, and statistical evidence; missing labels cannot be reconstructed from an answer key alone. Net primary production equals gross primary production minus plant respiration and represents biomass or energy made available for growth and consumers. Rates must be compared on the same area, biomass, leaf-area, and time basis because changing the denominator can reverse an apparent ecosystem ranking. Climate, nutrients, disturbance, species traits, and food-web structure interact, so broad ecological generalisations describe tendencies rather than universal rules.
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17-19