Which of the following is Bezout's identity?

• A
  $ax + by = \text{gcd}(a, b)$
• B
  $ax - by = \text{gcd}(a, b)$
• C
  $ax - by = \text{lcm}(a, b)$
• D
  $ax + by = \text{lcm}(a, b)$