You are presented with the quiz "What has a positive impact on a plant's roots' growth?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "the looseness of soil has a positive impact on a plant 's roots' growth in that soil" and "to improve soil, add several top-dressings of dirt or compost". 

So, what's the best answer to the question?


 

   looseness of dirt or compost        