The answer is D
One way to remember this is when you are building a bridge there is one piece right in the middle that keeps the whole thing from collapsing that is called the key-stone. If a keystone species goes extinct then the rest of the ecosystem will crumble around it.
Adenine pairs with thymine. They form complementary pairs withone another during replication of the parent strand, forming the complement strand. If thymine is present for 30% of the bases, then its complement, adenine, will also be present in 30% of the bases.
Vitamins are organic compounds that are essential in very small .or shortage of a vitamin may result in a vitamin-deficiency disease. Free radicals are formed not only through metabolic reactions .
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C. Light travels faster than sound
