Retail member firms that route orders to market makers in return for compensation:

a. are engaging in a prohibited practice under sec rules

b. is permitted to do so, subject to best execution requirements and disclosure requirements

c. must get the customer's oral consent prior to each trade

d. must get the customer's written consent prior to each trade

Retail member firms that route orders to market makers in return for compensation is permitted to do so, subject to best execution requirements and disclosure requirements, Option B.

Explanation:

If  a market maker is chosen by the retail market maker to "execute" its orders in return for "compensation", then this is the earning of that retail firm. It is called "payment for order flow". This practice is permitted by SEC with a condition that the retail member firm always executes its trades at the best available price. Also, the payments which are made for order flow must be revealed on customer confirmations. It is not engaging in any prohibited rules given by SEC , as per Option A and also there is no oral or written consent  required before each trade as per option C and D. So, Option B is correct.