Final answer:
The anterior muscles of the elbow, including the biceps brachii, brachialis, and brachioradialis, are used to raise a glass of water by flexing the forearm.
Step-by-step explanation:
The anterior muscles of the elbow are used to raise a glass of water. These muscles are responsible for flexing the forearm, allowing the hand to move closer to the body. The main muscles involved in the flexion of the forearm are the biceps brachii, brachialis, and brachioradialis.