Euclid relied on five basic axioms to build the propositions in his book Elements. The first axiom states, “Things that are equal to the same thing are also equal to one another.”

Which modern mathematical statement is equivalent to this axiom?

If a = b, then b = a.
If a = b and b = c, then a = c.
If a ≠ b, then b ≠ a.
If a = b, then a + c = b + c.