The correct answer is option 2: These treaties enabled the British to control the South Asian powers.

The Treaty of Yandaboo (1826), the Treaty of Salbai (1782), and the Treaty of Gandamak (1879) all share the common feature of giving the British control over South Asian powers.

In the Treaty of Yandaboo, the British East India Company signed an agreement with the Burmese Empire, which ended the First Anglo-Burmese War. This treaty allowed the British to control parts of Burma and establish British dominance in the region.

The Treaty of Salbai was signed between the Maratha Empire and the British East India Company. It ended the Second Anglo-Maratha War and gave the British control over significant territories in India.

The Treaty of Gandamak was signed between the British Raj and the Emirate of Afghanistan. It ended the Second Anglo-Afghan War and ensured British influence in Afghanistan`s internal affairs.

These treaties were all instrumental in enabling the British to expand their control and influence over South Asia, allowing them to establish colonial rule and exert dominance over various powers in the region.

Therefore, option 2 is the correct answer.