Answer:
The distance is
Explanation:
From the question we are told that
The smallest shift is 
Generally a grid unit is
of an arcsec
This implies that 0.2 grid unit is 
The maximum distance at which a star can be located and still have a measurable parallax is mathematically represented as

substituting values


Note 
So
11m/s Bc of the fact that he sees her running at 11m/s
In refraction, when a wave travels from one medium to another it changes speed.
Correct option is A.