What will be the output of the following $R$ code?

f function $($num $=1)\{$

hello "Hello world $\frac{?}{?}$

$"$

for $($i in seq$\_$len$($num$))\{$

cat $($hello$)$

$\}$

chars nchar$($hello$)*$ num

chars

$\}$

f $()$

a$)$ Hello world

$[1]12$

b$)$ Hello world

$[1]13$

c$)12$

d$)13$