The correct answer is: c) Both IDP and vehicle permits.
Foreign tourists driving in Sikkim must have an International Driving Permit (IDP) and a special vehicle permit. The IDP is a translation of your driver’s license into 12 languages, and it is required by Indian law for all foreign drivers. The special vehicle permit is required for all vehicles entering Sikkim, and it can be obtained from the Sikkim Tourism Department.
Option a) is incorrect because an IDP is not sufficient to drive in Sikkim. Option b) is incorrect because a special vehicle permit is not sufficient to drive in Sikkim. Option d) is incorrect because both an IDP and a special vehicle permit are required to drive in Sikkim.