Plants in the desert . A. effectively conserve and retain water
B. have high levels of transpiration
C. release 50-80% of water back into the ecosystem
D. make their own precipitation

A. Effectively conserve/retain water

Explanation:

Not only does this make the most logical sense, but it also is what plants in desert biomes actually do. Plants in the desert have made various adaptations to preserve their water, like by opening their stomata only at night or developing spikes to discourage animals from taking their water. I'm not sure if this is too much detail for you, but the plants in the desert that only open their stomata at night are called CAM plants, and other plants have made an adaptation so unique that they have their own name -- C4 plants, which utilize the relocation of CO2 to minimize water loss.

Further, B. is the opposite of conserving water, and C. is the opposite of conserving water. D. is just hilarious.

Hope this helped, cheers.

d. the weight of the book