Scientists believe that of species that once existed on earth are now extinct.
a. about three-quarters
b. nearly half
c. about 40%
d. over 99 percent

The correct answer is D. Over 99 percent

Explanation:

Life on Earth has existed for 4.28 billion ago and during this time billions of species have emerged including bacterias, fungi, plants, animals, etc. However, due to evolution, changes in the environment and massive extinction events most species that lived in other geological periods have completely disappeared or extinct. Indeed it is estimated by biologists and scientists that over 99% of the species that ever existed on Earth do not live today or are extinct this has been proposed based on the millions of fossils discovered that suggest multiple species that cannot be found nowadays and evidence that shows many more species are extinct and there is no or little evidence about them. Therefore over 99 percent of species that once existed on Earth are now extinct.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

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