Which of the following statements is correct regarding the disposal of shares by a shareholder?

a. When a shareholder sells shares to other shareholders, the corporation's capital base increases.

b. The sale of shares to other shareholders is known as a 'buy-back'.

c. The sale of shares back to the corporate treasury is not an allowable transaction.

d. The sale of shares to the corporate treasury may result in a deemed dividend and a capital gain or loss to the shareholder.