Because its air we cant see it thats why its clear because it would be scary if we were able to see air! :)
Answer:
Target heart rate is generally expressed as a percentage (usually between 50 percent and 85 percent) of your maximum safe heart rate. The maximum rate is based on your age, as subtracted from 220. At an 85 percent level of exertion, your target would be 145 beats per minute.
TPA is a medicine that is used in ischemia strokes to burst a clot.
