Which of the following statements are true?

1. Light does not need a medium to propagate.

2. The speed of light is the same in all frames of reference except for the one in which the observer is located.

3. The reason that relativistic effects are not commonly observed in everyday life is that relative velocities of objects are usually several orders of magnitude smaller than the speed of light.

4. Ether, if it existed, would act like the water in river-crossing problems.

plz explain

thank you