Asample of human dna consists of 30% adenine and 20% guanine. which is true about the remaining nucleotide
• a dna has 20% adenine and 30% guanine.
b dna has 30% thymine and 20% cytosine.
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c dna has 20% uradil and 30% cytosine.
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d. dna has 30% thymine and 20% uradil.

The correct answer is B) DNA has 30% thymine and 20% cytosine.

Explanation:

We use the Chargaff Law, where:

A + G = C + T (sum of pure bases A and G, is equal to pyrimidines C and T) and, A = T, C = G.

A + G = 30% + 20% =50% = C+ T

Thus:

A = 30% = T

G = 20% = C

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.