Question

what is a main plant adaptation in the desert biome?
both b and c
thick stems for water storage
large leaves
shallow roots

Explanation:

In desert biomes, water is scarce. Thick - stemmed plants (like cacti) can store water. Shallow roots help plants quickly absorb rainwater when it does rain. Large leaves would lose too much water through transpiration in a desert, so they are not a common adaptation.

Answer:

Both b (Thick stems for water storage) and c (Shallow roots) are main plant adaptations in the desert biome. So the answer is "Both b and c".