Explanation:

- The First Anglo-Afghan War began in the year 1839.

- This conflict arose from Britain's desire to prevent Russian influence in Afghanistan.

- Option 1: 1839 is the correct answer.

- During this year, the British entered Afghanistan to install a puppet ruler, Shah Shujah.

- The war lasted until 1842, characterized by significant losses for both sides.

- Option 2: 1840 is incorrect; it falls within the war period but is not the start year.

- Option 3: 1841 is incorrect; during this year, the British faced a revolt in Kabul.

- Option 4: 1842 is incorrect; this is when the British withdrew.

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