The French continued to pressure Siam, and in 1906-1907 they manufactured another crisis. This time Siam had to concede French control of territory on the west bank of the Mekong opposite Luang Prabang and around Champasak in southern Laos, as well as western Cambodia. France also occupied the western part of Chantaburi. In the Franco-Siamese Convention of 13 February 1904, in order to get back Chantaburi, Siam had to cede Trat to French Indochina. Trat became part of Thailand again on 23 March 1907 in exchange for areas east of the Mekong river including Battambang, Siam Nakhon, and Sisophon. The British interceded to prevent more French expansion against Siam, but their price, in 1909 was the acceptance of British sovereignty over Kedah, Kelantan, Perlis and Terengganu, under the Anglo-Siamese Treaty of 1909. All of these ceded territories were on the fringes of the Siamese sphere of influence and had never been securely under Siamese control, but being compelled to abandon all claim to them was a substantial humiliation to both king and country. In the early 20th century these crises were adopted by the increasingly nationalist government as symbols of the need for the country to assert itself against the West and its neighbours.
Question: How many regions was the acceptance of British sovereignty over according to the Anglo-Siamese Treaty of 1909?
Answer: 4