The correct answer is d: cDNA.
<span>cDNA or complementary DNA is DNA synthesized usually from messenger RNA (mRNA) by the enzyme reverse transcriptase. Because this molecule is from mRNA it contains only exons. cDNA is also produced naturally by retroviruses, for example, HIV virus.</span>
Group 7A, the Halogens contain metalloids such as Astatine.
Sorry but. Do your own school!
I believe they cannot start with big trees and bushes because the there is not enough nutrients in the soil, so instead pioneer species pave the way for primary succession.