What does Lin threaten to do if the British refuse to end the opium trade?​

Lin threatened to impose the death penalty on British merchants involved in the opium trade.

Explanation:

Lin Zexu (1785-1850), who had been appointed imperial commissioner in 1838, ordered British merchants to hand over their opium stock and stop the traffic of opium in China. The penalty for not following his command was death. The British superintendent of trade, Charles Elliot, refused the order, so Lin suspended all trade and took all foreign merchants hostage until Elliot surrendered and the merchants surrendered their stock, which was dumped into the sea.

would not cooperate with each other voluntarily.