Which statement about aerobic exercise is not true? select one of the options below as your
a. aerobic exercise strengthens the muscles that us breathe.
b. aerobic exercise is carried out for a sustained period of time.
c. regular aerobic exercise eliminates the risk of heart or lung disease.

C is not true. 

Regular aerobic exercise can REDUCE, but NOT eliminate the risks of heart or lung diseases

Well if you pick a machine to work on and that's gonna be your exercise if you don't stick to that machine your muscle strength your muscle mass rather will change because you haven't been doing it you change something in your exercise routine which changes your body's form of dealing with things for example you might become weaker or stronger depending on what kind of exercises you do in whether or not the machine you picked actually your muscles grow.