The correct answer is A. 4.2 seconds.
Alpha Centauri is the nearest star system to the Sun, at a distance of 4.37 light-years (4.1 x 1013 km; 2.5 x 1013 mi). It is a triple star system, consisting of three stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. Alpha Centauri A and B are both similar to the Sun in size and mass, and orbit each other every 80 years. Proxima Centauri is a smaller, fainter star that is much closer to Alpha Centauri A and B than they are to each other.
The light from Alpha Centauri A takes 4.2 seconds to reach Earth. This means that if you were to look at Alpha Centauri A right now, you would be seeing it as it was 4.2 seconds ago.
The other options are incorrect. Option B is incorrect because it is too long. Option C is incorrect because it is too short. Option D is incorrect because it is the distance between Alpha Centauri and Earth, not the time it takes for light from Alpha Centauri to reach Earth.