What did you learn about from the NASA's perseverance Rover land on Mars project?

NASA's Mars Pathfinder mission, launched in 1996, put the first free-moving rover—called Sojourner—on the planet. ... Together, these missions have shown scientists that Mars is an active planet that is rich in the ingredients needed for life as we know it—water, organic carbon, and an energy source

c)as speed changes, wavelength and frequency change.

everything changes!

a and b sometimes have a positive value