Explain how nitrogen oxides are produced and their environmental impact.

Nitrogen oxides are produced by the combustion engines in vehicles. Their effect on the environment includes both acid rain and smog.

these are common warning signs of overtraining syndrome:

washed-out feeling, tired, drained, lack of energy

mild leg soreness, general aches, and pains

pain in muscles and joints

sudden drop in performance

insomnia

headaches

decreased immunity (increased number of colds, and sore throats)

decrease in training capacity/intensity

moodiness and irritability

depression

loss of enthusiasm for the sport

decreased appetite

increased incidence of injuries.

a compulsive need to exercise

i say that the answer is 'd'