Final answer:
The nurse can assess if the needle is in a blood vessel by aspirating for a blood return, which involves pulling back on the syringe plunger after needle insertion.
Step-by-step explanation:
The correct action made by the nurse to assess whether the needle is in the client's blood vessel is c) aspirating for a blood return. This practice involves pulling back on the syringe plunger after needle insertion to see if any blood enters the syringe, which indicates that the needle may have entered a blood vessel. In such a case, the nurse would need to remove the needle and select a different site for injection.