Scientists must do what to be able to weigh substances to determine the what elements are present?

the answer is d. chordata

substitution is the answer in this case

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

carbon atoms, hydrogen, oxygen, and nitrogen.