input: Write a python function to detect query words from a sentence.
  assert detect_query("Can you give me a discount on this item?") == "discount"
  assert detect_query("I am looking for a special offer or discount.") == "discount"
  assert detect_query("Is there any sale or promotion available?") == ""
output: def detect_query(sentence):
      query_words = ["discount", "sale", "promotion", "offer"]
      words = sentence.lower().split()
      for word in query_words:
          if word in words:
              return word
      return ""