Immunoglobins, i believe. :)
The third and last option is correct.
Species in the past (referring to dinosaurs) were more massive.
levels where higher in the past, which meant that plants prospered during that time since they had a easy access to food. That contributes to the fact that herbivores could grow bigger because there was more food. Which in turn, increases the size of early carnivores which eat bigger herbivores.
Hope it helped,
Happy homework/ study/ exam!
