input: Write a python function to extract all the first elements from a list of lists.
  assert extract_first_elements([["apple", "french fries"], ["banana", "rice"], ["carrot", "salad"]]) == ["apple", "banana", "carrot"]
  assert extract_first_elements([["dog", "cat"], ["lion", "tiger"], ["fish", "shark"]]) == ["dog", "lion", "fish"]
  assert extract_first_elements([[1, 2], [3, 4], [5, 6]]) == [1, 3, 5]
output: def extract_first_elements(list_of_lists):
      return [sublist[0] for sublist in list_of_lists]