Explanation:

- Perfect Competition (Option 1):

- Many firms, identical products.

- No single firm can influence the market price.

- Trusts and cartels are not typically formed here.

- Monopoly (Option 2):

- Single firm dominates the market.

- No competition to form trusts or cartels.

- Firm already controls the market.

- Oligopoly (Option 3):

- Few firms dominate the market.

- High potential for collusion and formation of trusts or cartels.

- Firms may cooperate to set prices or output.

- None of them (Option 4):

- Implies none induce trusts or cartels.

- Not applicable in markets like oligopoly.

- Correct Answer: Oligopoly (Option 3)