Passage: Sulu is a part of the Sulu Archipelago, which stretches from the tip of the Zamboanga Peninsula on the north to the island of Borneo in the south. The main island and its islets are situated between the island-provinces of Basilan to the northeast, and Tawi-Tawi to the southwest. Sulu is bordered by two seas; the Sulu Sea to the north, and the Celebes Sea to its south. Sulu has over 157 islets, some of which remain unnamed.

Question: What island-province is to the southwest of Sulu?
Tawi-Tawi