Why ovulation does not occur when the uterine lining is not at it's thickest?

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

it should be d) transitional fossils.

they show the gradualism of evolution throughout a period of time