The normal PR interval is between:

a$.$

$0\mathrm{.}8$ and $0\mathrm{.}24$ seconds

b$.$

$0\mathrm{.}8$ and $0\mathrm{.}16$ seconds

c$.$

$0\mathrm{.}12$ and $0\mathrm{.}20$ seconds

d$.$

$0\mathrm{.}10$ and $0\mathrm{.}24$ seconds