Given that $x \le -7,$ identify all the correct conclusions.
(A) $3x \le -21.$
(B) $3x \ge -21.$
(C) $-3x \le 21.$
(D) $-3x \ge 21.$
Enter the letters of all the conclusions that are correct (separated by commas). For example, if you think that conclusions B and D are correct, say "B, D".