Explanation:

1, 2 and 3

Countries initiate anti-dumping probes to determine if the domestic industry has been hurt by a surge in below-cost imports.

This statement is correct. Anti-dumping investigations are initiated by countries to assess whether the domestic industry has been harmed by a sudden influx of imports at prices below their fair market value.

These duties are imposed under the multilateral WTO regime.

This statement is correct. The World Trade Organization (WTO) provides a framework for countries to impose anti-dumping duties as a measure to address unfair trade practices.

Anti-dumping measures are taken to ensure fair trade and provide a level-playing field to the domestic industry.

This statement is correct. The primary purpose of anti-dumping measures is to counteract unfair trade practices, promote fair competition, and protect domestic industries from harm caused by below-cost imports.

Therefore, the correct option is 4 (1, 2, and 3).