in a single polymerase chain reaction (pcr) cycle consisting of 15 seconds at 94°c, 30 seconds at 50°c, and 1 minute at 72°c, what is happening in the step run at 50°c?

Which of the following is a physical change? a.burning a piece of wood b.sawing a piece of wood in half c.rust forming on an iron fence d.a copper roof changing color from orange to green