Given below are two statements.
One is labelled as Assertion A and the other is labelled as Reason R.
Assertion (A) : Late wood has fewer xylary elements with narrow vessels.
Reason (R) : Cambium is less active in winters. 

In the light of the above statements, choose the correct answer from the options given below:

Assertion (A) is true. In winter, the cambium is less active and forms fewer xylary elements that have narrow vessels, and this wood is called autumn wood or late wood. In the spring season, cambium is very active and produces a large number of xylary elements having vessels with wider cavities. The wood formed during this
season is called spring wood or early wood. 
Reason (R) is also true. Cambium is less active in winters so that fewer xylem vessels are formed and vessels are narrow. 
Reason (R) is the correct explanation for Assertion (A).