How many minutes must the target heart rate be maintanied in order for aerobic exercise to be beneficial

How do the uv rays cause damage?   what exactly causes the skin to burn;   can you be more specific about this mechanism?   3. how do photosensitive medications increase a person's sensitivity to sunlight and therefore increase their risk of getting burned?     what kind of medications can increase photo-sensitivity, can you think of some examples?

Bella is reporting the pulse (heartbeats per minute) of a patient. which symbol is most useful for her? a. ’ b. “ c. # d. / e. ^

Which is a physical sign of stress? a: unexplained euphoria b: feelings of invincibility c: inability to sleep d: visual hallucinations