Which statement about the internationalization process model, also known as the Uppsala model, is correct?

a$.$

The model was inspired by a study of USA companies expanding first to Canada, and then to countries further afield.

b$.$

The model suggests companies have to go through certain specified stages when developing their international business operations.

c$.$

Commitments to higher degrees of involvement in a foreign market depend on the knowledge acquired by the firm up to that time.

d$.$

The model mainly applies to mature multinational enterprises.