input: Write a python function to replace all consonants in a string with underscores.
  assert replace_consonants("Hello World") == "He__o _o__d"
  assert replace_consonants("Python") == "_y__o_"
  assert replace_consonants("Programming") == "_ro__a__i__"
output: def replace_consonants(s):
      vowels = "aeiouAEIOU"
      return ''.join(['_' if char.isalpha() and char not in vowels else char for char in s])