input: Write a function to return a matrix C where each element is the product of the corresponding elements of matrices A and B.
  assert elementwise_multiply([[3, 4], [1, 2]], [[7, 5], [0, 1]]) == [[21, 20], [0, 2]]
  assert elementwise_multiply([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[5, 12], [21, 32]]
  assert elementwise_multiply([[0, 0], [0, 0]], [[1, 1], [1, 1]]) == [[0, 0], [0, 0]]
  assert elementwise_multiply([[2], [4]], [[3], [5]]) == [[6], [20]]
  assert elementwise_multiply([], []) == []
output: def elementwise_multiply(A, B):
      return [[A[i][j] * B[i][j] for j in range(len(A[i]))] for i in range(len(A))]