The correct answer is: a) Restrict outsider entry and protect tribal lands.
The Inner Line Permit (ILP) system was introduced in the Lushai Hills by the British in 1873 to restrict the entry of outsiders into the region and protect the tribal lands. The ILP system is still in place today, and it requires all non-tribal people to obtain a permit before entering the region. The permit system is designed to protect the culture and way of life of the tribal people, and to prevent the exploitation of their resources.
Option b) is incorrect because the ILP system was not introduced to suppress uprisings. The ILP system was introduced to protect tribal lands, not to suppress uprisings.
Option c) is incorrect because the ILP system was not introduced to promote tea plantations. The ILP system was introduced to protect tribal lands, not to promote tea plantations.
Option d) is incorrect because the ILP system was not introduced to facilitate Christian missionary work. The ILP system was introduced to protect tribal lands, not to facilitate Christian missionary work.