List 3 characteristics of x-rays that are useful to physicians in the diagnosis and treatment of disease

1) ability to cause exposure of a photographic plate
2) ability to penetrate different substances to varying degrees
3) invisibility
invisible waves of energy that are produced by an energy course and are useful in the diagnosis and treatment of disease. 

Push up require upper body strength, so weight-training exercises such as shoulder press, curl ups and dead lifts would improve your ability to perform proper push ups.