Under the Han, iron and salt were so important that

To gain funds is the correct answer.

Explanation:

In China, salt and iron were produced by private industry, but emperor Wu established government monopoly in their trade. He started government monopoly in grain trade to raise funds. An agency was set up for this, whose purpose was to gain profit for the government and discouraging private trade. Excise taxes were imposed on liquor too. During those times the government distrusted private markets and their profits. Emperor Wu died in 87 BC.

Under the Han Dynasty, iron and salt were so important that Emperor Wudi established salt and iron monopolies and new taxes were decreed.