When the human arm is bent, the state of the upper arm muscles is that:

1. The biceps and triceps lie in the upper arm and work as an antagonistic pair. 2. Antagonistic means they oppose one another, so when one contracts the other must relax. 3. Bending the arm requires the biceps to contract, pulling the forearm upwards. 4. The triceps therefore relaxes at the same moment. 5. Because they are a pair, the two can never both contract or both relax, which rules out the last two options. _Source: NECTA CSEE 2022 Biology 033, Question 1: Multiple Choice Items, item (ix)_