Which of the following levels is the most efficient at energy conversion?
a. producers
b. primary consumers
c. secondary consumers
d. tertiary consumers

The correct answer is A) producers. That is because they create the energy themselves and don't waste that much. Primary eat those plants so they only take a part of the produced energy, while the secondary eat them and then have even less energy, and the tertiary get the least. Primary ones get the most energy compared to what they make and lose.