Consider the following statement regarding “Generic Medicine”?

1. They are unbranded drugs.

2. They can be produced for only those drugs for which the product patent has been expired.

3. Once the product patent is introduced, generic manufacturers can't continue except when they pay a fee (royalty), if the patent holder agrees.

4. They cannot be sold at a price less than the actual price of the medicine.

Which of the statements given above is/are correct?