I think it'd be B.. I might be wrong tho..
Ok I will help you I just gotta look it up real quick
<span>Circadian rhythm</span>, also known as circadian clock or body clock is a biological process that follows a 24 hour cycle (approximately). It is said that circadian rhythm is dictated by natural factors in the body, as well as environmental signals.
Different enzymes have specific active sites which can only catalyze one <span>substrate. Enzyme-substrate complexes are produced only when the substrate fits into the active site :)</span>