Why all the units are checked every two years by the government

Ibelieve that the correct answer is: c. along plate boundaries

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.

Imma say go with a (:

We can infer that star y is closer but other factors must be considered including the heat of the star, the mass, and the brightness of the star. even though star x seems dimmer it may just be less bright or contain less heat.