Which HTML form control allows users to select only one option from a set?

a$.$

b$.$

$<$select$-$option$>$

c$.$

$<$input type$=$"checkbox"$>$

d$.$

$<$set$>$

e$.$

$<$input type$=$"radio"$></$p$></$div$><$div$></$div$>$