Which statement about human beings' absolute threshold is correct?
O a. After not eating or drinking for 1 hour, humans can taste 5 milligrams of sugar in a gallon of water
O b. In a clean environment, humans can smell a drop of perfume from 4 feet away
O c. In the dark, humans can see light from a candle from 30 miles away
O d. In a quiet environment, humans can hear a watch ticking from 20 miles away