How could a cactus adapt to its dry environment?

What is used to keep track of the gamates and possible offsprings combination

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic

The source of energy shown in the image is (renewable, non renewable, polluting) a drawback of building a dam is that (it will destroy ecosystems, it requires fossil fuels, it won’t be useful for irrigation)