What Is the Difference Between the Base_grand_total and Grand_total Attributes

What is the difference between the base_grand_total and grand_total attributes of the order?

A) base_grand_total is a grand total before tax is applied; grand_total is the grand total after tax is applied.
B) base_grand_total is the grand total at the moment of order submission; grand_total is the grand total at the moment of order closing.
C) base_grand_total is the grand total in the currency of the store where the order was submitted; grand_total is in US dollars always.
D) base_grand_total is in a base currency and grand_total is in the currency of the website where the order was submitted.