1.ans
The best explanation of why viruses are not classified by the Linnaean taxonomy is due to C. the Virus can't reproduce outside of a host cell, which means that the host is necessary for its survival and reproduction, and without it cannot live on its own accord, so they are considered non-living, that can't metabolize and undergo the essential reactions of their own.
2.ans
Because both domains are capable of sharing segments of DNA with unrelated organisms which makes genetic classification difficult.
3.ans
It would make it possible to compare that species to other species at a level deeper than outward appearance
The proteins like hemoglobin and enzymes can be studied to see whether organism which are similar in form can also be related to each other. Its differences found in these proteins' amino acid sequences will present how closely or distantly related an organism is to another.