Fall is my favorite season of the year.

It is when all of the trees turn vibrant shades of red, orange, and yellow.

What is the BEST way to combine the two sentences?
A) My favorite season of the year is fall, when all of the trees turn vibrant shades of red, orange, and yellow.
B) When all of the trees turn vibrant shades of red, orange, and yellow, it is fall, my favorite season of the year.
C) All of the trees turn vibrant shades of red, orange, and yellow in the fall, which is my favorite season of the year.
D) Fall is my favorite season of the year, and it is when all of the trees turn vibrant shades of red, orange, and yellow.