How could a cactus adapt to its dry environment?

Which statement is true about the cell theory? a) it is well-supported by evidence. b) it is unchangeable and permanent.

Which of the following are causes of evolutionary change? 1)genetic drift 2) natural selection 3) gene flow 4)mutation

Kidney stones are tiny crystals of calcium or magnesium that block the narrow sections of the excretory system. which symptoms would a person with kidney stones experience? a. inability to store urine; pain in the bladder b. inability to store urine; pain in the urethra c. reduced urine flow; pain in the bladder d. reduced urine flow; pain in the urethra