input: Write a function that takes a list of strings and a separator as input, and returns the concatenation of all the elements with the specified separator.
  
  def concatenate_strings(strings, separator):
      return separator.join(strings)
  
  assert concatenate_strings(["Sample","Text","Hello"], "-") == "Sample-Text-Hello"
  assert concatenate_strings(["Python", "is", "great"], " ") == "Python is great"
  assert concatenate_strings([], "|") == ""
  assert concatenate_strings(["One"], ",") == "One"
  assert concatenate_strings(["A", "B", "C"], "/") == "A/B/C"
output: def concatenate_strings(strings, separator):
      return separator.join(strings)