How does an enzyme influence a biological reaction? It decreases the kinetic energy of reactants, enabling them to undergo chemical change more
easily.
It decreases the activation energy necessary to initiate the chemical change.
It weakens the bonds of reactants, making them easier to break.
It increases the kinetic energy of reactants, thereby increasing their tendency to collide.
It increases the net energy difference between reactants and products.

B. It decreases activation energy.

Explanation: A regular reaction has high activation energy required for the reaction to occur. Enzymes act as catalysts that decrease activation energy and speed up the reaction.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;