Which AS path regular expression will only match a route originating in AS 500 with the last traversing AS of 100?

Which AS path regular expression will only match a route originating in AS 500 with the last traversing AS of 100?

A.
“$100 .* ^500”

B.
“500 .*”

C.
“^100 .* 500$”

D.
“^100 .*”