Five KM values are given for the binding of substrates to a particular enzyme. Which has the strongest affinity when k$1$ is greater than k$2?$

a$.$

$0\mathrm{.}15$ mM

b$.$

$1\mathrm{.}5$ nM

c$.$

$150$M

d$.$

$15000$ pM

e$.$

$150$ mM