If a certain combination of goods and services lies inside the production possibilities curve for an economy, which of these statements must be true?

You can drink laxative, or  do this exercise when you are sitting in the bathroom on the toilet. to relieve  constipation  fast or in about 1 minute, pinch your nose after your usual exhalation. start holding your breath. but do not mouth breath during this just hold your breath. 

C; skin, is the answer!