input: Write a function to determine if the first string contains the second string. If it contains the second string, return True; otherwise, return False.
  assert check_contains("catering", "cat")==True
  assert check_contains("catering", "dog")==False
  assert check_contains("catering", "ing")==True
  assert check_contains("catering", "catrin")==False
  assert check_contains("", "cat")==False
output: def check_contains(s1, s2):
      return s2 in s1