input: Write a function to add a string at the beginning of each string in a list.
  assert add_string_beginning(['Red', 'Green', 'Black'], 'White') == ['WhiteRed', 'WhiteGreen', 'WhiteBlack']
  assert add_string_beginning(['Apple', 'Banana', 'Cherry'], 'Fruit: ') == ['Fruit: Apple', 'Fruit: Banana', 'Fruit: Cherry']
  assert add_string_beginning(['Dog', 'Cat', 'Mouse'], 'Animal: ') == ['Animal: Dog', 'Animal: Cat', 'Animal: Mouse']
output: def add_string_beginning(lst, prefix):
      return [prefix + s for s in lst]