Already before the market opens in the morning, a pro order comes in from a colleague to purchase 5,000 shares at market price. Immediately afterwards (still before the market opens) a client order comes in to purchase only 500 shares at market price. Which of the following is the correct?

a. The client order will receive priority.

b. The pro order will receive priority because it was received first.

c. The pro order will receive priority because it is for a greater number of shares.

d. The trader has the discretion about which order to execute first or to bundle them given that the market is not even open yet and may even get a better price for both parties as one transaction.