2. To focus a microscope using the high power lens you must first in low power center the specimen and make sure it is in focus. Then switch to high power and adjust using the fine adjustment or the smaller knob.
3. It prevents dust from settling on the scope and in the lenses.
Based on the attached Image;
The two species that are likely to have the most similar DNA base sequences
are C and D. An evolutionary tree or a phylogenetic tree, like the one shown on the image is used to indicate which ancestors gave rise to which descendants. The tree represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa. The tips of the tree represents groups of descendant taxa and the nodes represents the common ancestors of these descendants.
Viruses aren't made out of cells.