Execute the topological sort algorithm provided in the lecture on the following directed graph. If

there is a choice handle vertices in alphabetic order.

Q$1.$TO: vertices $1--4$

Give the first four vertices of the topological ordering as a string without separators. Your answer should be a string consisting of four of the letters from a$-$p without separators. For instance, if you think that the the first four vertices of the topological ordering are i$,$ j$,$ k$,$ and l$,$ then your answer should be ijkl.

Q$2.$ vertices $5--8$

Give the next four vertices of the topological ordering as a string without separators.

Q$3$ TO: vertices $9--12$

Give the next four vertices of the topological ordering as a string without separators.

Q$4.$ TO: vertices $13--16$

Give the next four vertices of the topological ordering as a string without separators.