Stress can actually improve your ability to concentrate and perform if the level is

Stress is like a battle that one has to fight in order to meet the demands and expectations of the peers. This battle work really well for those who perform best under pressure/stress but it can really get on the nerves of those to tend to work patiently without being bothered. Keeping both scenarios together, the level of stress must be kept on moderate level, so that both the working conditions can be facilitated and does not becomes a nightmare of any.

what effect does exercise have on the nervous system?

the answer is c.