input: Write a function to generate a random string of a specified length using lowercase letters. The function should accept the length of the string as an input parameter and return the generated string.
  assert random_string(6)=="abcdef"
  assert random_string(6)=="ghijkl"
  assert random_string(6)=="mnopqr"
  assert random_string(6)=="stuvwx"
  assert random_string(6)=="yzabcd"
output: import random
  import string
  
  def random_string(length):
      return ''.join(random.choices(string.ascii_lowercase, k=length))