The correct answer is: A. exercise restraint.
The soldiers were instructed to exercise restraint, which means to control their emotions and actions. This is important because it helps to prevent violence and ensure that the situation is handled peacefully.
The other options are not as accurate. Option B, control, is similar to restraint, but it implies a more forceful approach. Option C, prevent, is not accurate because the soldiers were not instructed to prevent the situation from happening. Option D, enforce, is not accurate because the soldiers were not instructed to enforce any laws or regulations. Option E, remain, is not accurate because the soldiers were not instructed to remain in a specific location.
In conclusion, the correct answer is A. exercise restraint.