Health economics class

One major premise of the Rothschild-Stiglitz model is that there is a perfectly competitive market for health insurance. a. What is it about competition that prevents pooling in the Rothschild-Stiglitz model? b. Suppose instead that the market is not perfectly competitive, and in fact competitor firms have a hard time entering the market. Could a pooling equilibrium occur in this case? c. "Competition in health insurance markets is harmful." Evaluate this statement