input: Write a python function to compute word frequency in a sentence.
  assert compute_word_frequency("hello world hello") == {"hello": 2, "world": 1}
  assert compute_word_frequency("test the function test it well") == {"test": 2, "the": 1, "function": 1, "it": 1, "well": 1}
  assert compute_word_frequency("one fish two fish red fish blue fish") == {"one": 1, "fish": 4, "two": 1, "red": 1, "blue": 1}
output: def compute_word_frequency(sentence):
      words = sentence.split()
      frequency = {}
      for word in words:
          if word in frequency:
              frequency[word] += 1
          else:
              frequency[word] = 1
      return frequency