A

```
"""Topological Sort."""
# a
# / \
# b c
# / \
# d e
edges: dict[str, list[str]] = {
"a": ["c", "b"],
"b": ["d", "e"],
"c": [],
"d": [],
"e": [],
}
vertices: list[str] = ["a", "b", "c", "d", "e"]
def topological_sort(start: str, visited: list[str], sort: list[str]) -> list[str]:
"""Perform topological sort on a directed acyclic graph."""
current = start
# add current to visited
visited.append(current)
neighbors = edges[current]
for neighbor in neighbors:
# if neighbor not in visited, visit
if neighbor not in visited:
sort = topological_sort(neighbor, visited, sort)
# if all neighbors visited add current to sort
sort.append(current)
# if all vertices haven't been visited select a new one to visit
if len(visited) != len(vertices):
for vertice in vertices:
if vertice not in visited:
sort = topological_sort(vertice, visited, sort)
# return sort
return sort
if __name__ == "__main__":
sort = topological_sort("a", [], [])
print(sort)
```