The vascular cambium
a. is part of a plant's secondary growth
b. produces secondary phloem and xylem tissue
c. increases in ring size each year
d. all of the above

d. all of the above. Vascular cambium is initiated during secondary growth. These tissues form secondary phloem and xylem. Intrafascicular and interfascicular cambiums represents a continuous ring and is called the cambium ring.

The correct answer is c