Consider the following statements regarding the economy of medieval India:

1. The introduction of the Persian wheel and improved irrigation systems increased agricultural output.
2. Trade in precious metals was largely confined to domestic markets during the medieval period.
3. Agrarian surplus played a key role in supporting urban centers, leading to the growth of towns.
4. Guilds of artisans played an important role in regulating production and trade.

Which of the above statements is/are correct?