Why does dna need to be copied into mrna?

mRNA will serve as reference book that contains information as the DNA and its sequence is complementary to the DNA template.

The transfer of information in a DNA strand to a new molecule of messenger RNA is known as transcription. Thus, the process of transcription is carried out by an enzyme called RNA polymerase and a number of accessory proteins called transcription factors. However, DNA is copied into mRNA because mRNA will serve as reference book that contains information as the DNA and its sequence is complementary to the DNA template.

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.