Acactus with long spines protects itself from animals better than a cactus with short spines. according to natural selection,
short-spined cacti will survive longer and reproduce more often than long-spined cacti
long-spined cacti will survive longer and reproduce more often than short-spined cacti
over time, the population will become entirely made of short-spined cacti
over time, cacti with long spines will completely die out

long-spined cacti will survive longer and reproduce more often than short-spined cacti

Explanation:

The natural selection is the process of differential survival and reproduction which is facilitated by beneficial traits that some living beings posses over the others. These traits help these living beings to survive and reproduce. Thus the beneficial traits are passed on from generation to generation.

The long spines prevent the herbivorous eating better than the short spines. Thus the long spine cactus will survive and reproduce more than the short spined cactus.      

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yes its like the dead sea which is full of salt which makes you stay afloat

so yes an egg will float in salt