What does A DOUBT mean in brain teasers?

How many units of insulin are in a mililiter? What enzyme digest protein? Does orphenadrine citrate contain sulfa? When do capillary beds open and close? Are these organs in the digestive system made of muscle? What is a circumscribed nodule in the lung? Why does sinus drainage irritate vocal cords? Can a tooth ache be cured by milk? What is resting heart rate for a female 73 years not taking any medicine? Does smoking worsen a sinus infection? Where is the hepatic pedicle? Is there a name for social phobia? Is articulation a example of musical parameter? What part of digestive system that softens the food? If you are homeschooled and your mother contacted a therapist who said you have severe depression and anxiety but your mother refuses to get you help beyond that diagnosis what can you do? What are the Medicinal Properties of Aloe Ferox? How urine is removed from the blood and then eliminated from the body? Why does blood always go through the liver from the gut prior to returning to the heart? Can redbull increase girth? What is the longest time anybody stayed up on a one night sleep over?