What is the smallest worst$-$case asymptotic runtime of the following loop $($i$.$e$.$ the tightest bound$)?$

for j$1$ to n do

if j mod n $=0$ then

for k$1$ to j do

sum $$ sum $+1$

Question $43$ options:

O

$($

$1$

$)$

O

$($

log

n

$)$

O

$($

n

$)$

O

$($

n

$2$

$)$

O

$($

n

$3$

$)$

O

$($

n

$4$

$)$

O

$($

n

$5$

$)$