input: Write a function to find the word that appears most frequently in a list of input strings.
  assert find_most_frequent_word(["UTS is best for RTF", "RTF love UTS", "UTS is best"] ) == 'UTS'
  assert find_most_frequent_word(["Its been a great year", "this year is so worse", "this year is okay"] ) == 'year'
  assert find_most_frequent_word(["Families can be reunited", "people can be reunited", "Tasks can be achieved"] ) == 'can'
output: def find_most_frequent_word(input_list):
      from collections import Counter
      words = []
      for sentence in input_list:
          words.extend(sentence.split())
      most_common_word, _ = Counter(words).most_common(1)[0]
      return most_common_word