Please choose the correct answer and explain the solution.

13. (Problem 7) Choose ALL correct statements, if more than one is correct. (10 Points) D (A) The decimal representation for hex number FF is 255. (B) For any integer n > 0, the greatest common divisor gcd(n, 2021) = gcd(n, 2021 mod n). (C) In order to nd the inverse of b (mod a), we may first nd E] integers x and y so that ax + by = I. Then the inverse of b (mod a) is y. C] (D) The encrypted letters for \"CDE\" using encryption function for) = x 5 (mod 26) is "XYZ". [:I (E) None of the above is correct