When an Employee Stock Option Is Exercised,which of the Following

When an employee stock option is exercised,which of the following is usually true?

A) The employee pays the market price for the shares and the company refunds the difference between the market price and the strike price
B) The company or the company's agent buys stock in the market for the employee
C) The company issues more shares and sells them to the employee for the strike price
D) The employee cannot immediately sell the shares