Questions on Topological Sorting
The comments are right. In a topological sort, we start with nodes that have no incoming arrows and remove them from the graph, so to speak. In this case, if there are multiple possible nodes to remove, then we want to remove them in lexicographical order. Hence, the order should be $B, A, C, D, E , F, G, H$.

Your suggest topological sort does not work. This is because you propose to put $G$ before $F$.