Gated ion channels: a. transmit electrical signals.
b. only allow passage of Na+ and K.
c. open or close based solely on changes in membrane potentials.
d. allow passage of neurotoxins into cells.

that is wrong, its not thymus.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.

the answer is 100% density i've answered this question before and done the quiz myself.