At what current level is it true that an electric shock victim is NOT able to let go?

The correct choice indicates that at a current level of 20mA, an electric shock victim is typically unable to let go of the source of the electric shock. This phenomenon is primarily due to the way electrical current affects muscle contractions in the body. When the electrical current passes through a person, it can cause involuntary muscle contraction. At around 20mA, which falls within the range identified as the threshold for this effect, the muscles, particularly in the hand, contract so tightly that the individual cannot release their grip on the electrified object.

Current levels below this threshold (around 10mA) may still allow for voluntary control, meaning that the victim could potentially pull away from the source. As current levels increase towards 30mA and beyond, the risk of serious injury and potential fatality increases significantly, as these levels can cause more severe physiological reactions, including ventricular fibrillation or serious injury to internal organs.

Understanding these current thresholds is crucial for safety practices in electrical work, where minimizing exposure to electrical currents is essential for preventing accidents and ensuring the safety of individuals working with or near electrical systems.