Fact 1: Secondary meristem is located within and around the vascular tissues. Fact 2: Secondary meristems make the stem or root grow larger in diameter. Given the two facts above, what make the stem or root grow larger in diameter?

Select from the following.
1). heart cells
2). rainfall
3). bending light rays
4). vascular tissues
5). tissue boxes
6). plant cells
7). colors of the spectrum
8). Exfoliation
Answer:
4).