[Physics] Confusion with the equivalence principle and inertial frames

Question

This is an explanation of the equivalence principle. A. says accelerating frames can simulate gravity. Then, I am confused. Are the frames presented in A. inertial frames? Compared to B. I have the impression that the frames in A. are not inertial frames. Then, does it mean that any observer standing on earth is not an inertial observer? But this is contrary to my common sense… Also, the Einstein's postulate says that the speed of light is same in all inertial frames. Then, the speed of light measured from frames in A are not equal to $c$?

Answer 1

Are the frames presented in A. inertial frames?

No, the frames are accelerated reference frames - an accelerometer at rest in either frame reads non-zero acceleration - and not inertial reference frames.

Then, does it mean that any observer standing on earth is not an inertial observer?

Yes, an accelerometer attached to an observer at rest on the surface of the Earth reads non-zero acceleration and so the observer's reference frame is an accelerated reference frame and not an inertial reference frame.

Then, the speed of light measured from frames in A are not equal to c?

You might find the answers here useful: Does the speed of light vary in non-inertial frames?