Consider the following statements regarding economic activities in the Indus Valley Civilization sites in Punjab:

1. Bead-making workshops have been discovered at sites like Sanghol and Sunet, indicating specialized craft industries.

2. The Harappans practiced slash-and-burn agriculture due to poor soil fertility in the region.

3. The presence of copper artifacts at sites like Ropar and Sanghol suggests long-distance trade with Rajasthan and beyond.

4. The Harappans used a standardized system of weights and measures for trade.

Which of the above statements are correct?