Althogh options are not given for this question, here is what I can speculate based on provided limited information.
Temperate grasslands have few trees and large shrubs (mostly absent). Here, <u>grasses are the main vegetation</u>. A major reason behind this is the <u>low average annual precipitation</u> which doesn't allow bigger plants to survive.
For the second part I can say that temperate grasslands have primary vegetation (grasses) whereas other biomes have higher plants as well.