A or B maybe D I had this question on a test before.
A then b i think
<3 hope this helps
Solution :
The semi-major axis of any terrestrial body may be defined as equal to mean distance of the body, so that the cube of its mean distance of the planet is directly proportional to the square of the sidereal period.
It is given by Kepler's third law,

where p is the orbital period
a is the semi major axis
Given :
a =
m
Therefore, a =
m
= 3.3 AU
So, 

p = 6 years (approximately)
or p =
seconds ( since, 1 year =
seconds )
I would say mostly economic factors: common currency, common market, wide-scale trade among the countries. If one country is hit, the others will also suffer: this brings in the feeling of solidarity.
other than that, European culture is actually quite unified, with many shared valued, such as universal health care and religious freedom, yet connection to Christianity.