input: Write a python function to initialize a 2D array with zeros.
  assert initialize_array(3, 4) == [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
  assert initialize_array(2, 2) == [[0, 0], [0, 0]]
  assert initialize_array(1, 5) == [[0, 0, 0, 0, 0]]
output: def initialize_array(rows, cols):
      return [[0 for _ in range(cols)] for _ in range(rows)]