Consider the following variable$-$length code for the following eight letter alphabet:

$\backslash$table$[[$Symbol$,\backslash$table$[[$Binary$],[$Code$]]],[$a$,01110],[d,10],[g,001],[$j$,111],[$m$,000],[$p$,11001],[$s$,00010],[$v$,11000]]$

Which of the following changes will make this a prefix$-$free code? $($Pick $a$ if no changes are necessary.$)$

None $($It is already a prefix$-$free code$).$

Change the code for $a$ to $1101.$

Change the code for $j$ to $1101.$

Change the code for $m$ to $100.$

Change the code for $s$ to $01010.$