EXPLANATION #2
the question now becomes, train though experiment or twins paradox
if for trains:
spaceship measures 10 years (given)
spaceship views earth as 6 years
earth measures 10 years
earth views spaceship as 6 years
since both perspectives are as valid as the other, earth is 6 years with the perspective of the spaceship (that's the perspective the question asked)
therefore B is correct
for twins paradox:
spaceship measures 10 years (given)
spaceship views earth as 6 years
earth measures 10 years
earth views spaceship as 6 years
since in twins paradox, spaceship comes back, earths perspective is taken preference, therefore the people on earth are older than the people in the spaceshit, BUT it's 10years older for earth people, 6 years older for space people
therefoe C is correct
so now that i look at it, D can't possible be correct, oh well i lose a mark