How could testing milk that's past its expiration date introduce bias?

For the car in the picture ,in which direction is the normal force? -into the screen -down -out of the screen -up

Which additional product balances the reaction h2so4 + 2naoh → na2so4 + 2h2o 2oh h2o2 h3o

Adolphin emits ultrasound at 100khz and uses the timing of reflections to determine the position of objects in the water. part a what is the wavelength of this ultrasound? assume that temperature of water is 20 degrees c. answer in cm