What adaption allows the cactus to thrive ? needles to prevent dying out ..or deep roots to absorb ground water?

The answer would be deep roots to absorb ground water.

Cacti are found in deserts, which do not receive much rain.  Cacti, like all plants, need water to live so deep roots would help the cactus obtain water.

Hope this helps!

blue stars have the highest surface temp

stellar distances are usually expressed in light-years

the measure of a star's brightness is called magnitude

hope this !

it would be heredity