Final answer:
To correct the problem of an unacceptable motor response in the sartorius muscle during an FNB, the needle should be withdrawn to reposition it away from the nerve.
Step-by-step explanation:
The correct action to correct the problem of an unacceptable motor response in the sartorius muscle during a Femoral Nerve Block (FNB) would be to withdraw the needle slightly to reposition it away from the nerve. This can help to avoid directly stimulating the nerve and causing the motor response. Increasing the volume of local anesthetic injected may not be necessary and can increase the risk of complications. Proceeding with the block as planned and considering the motor response as normal would not be appropriate. Injecting a neuromuscular-blocking agent to suppress the motor response is not recommended in this situation.