$(2)$ For this part, you only have to write or draw the answers to the following questions $($i$.$e$.,$ no explanations needed$).[6$ marks total for this part, $1$ mark each$]$

a$.$ Convert the following string $($in pre$-$order of an arithmetic expression$)$ to a strict binary tree: $**+-$bca$-**$ e $fd$

Answer: