Solutions
Let us note the following:
An assumption is a fact that is accepted without any proof.
It cannot be deduced directly from the passage.
The author is trying to understand the effect if the earth stops spinning.
Thus the author has by default accepted the rotation of earth without any proof.
So, option (A)is the correct assumption.
The option (C) finds a direct mention in the passage
So, it is not an assumption.
The option (B) sound more like a negative random conclusion.
Therefore, option (B) is not an assumption.
Therefore, the correct answer is 'The earth had been in rotation continuously since long'.
Hence, the correct option is (A).