You are presented with the quiz "What can be checked along with nutrition and scion that can help determine health of a tree." 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "the number of rings in a tree trunk can be used to estimate the age of the tree" and "tree age, scion, nutrition and other factors that affect the overall health of the tree could affect rootstock resistance or susceptibility to Phytophthora". 

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


 

 the number of rings          