A king should be a hero because he can protect you from terrorist attacks
I'd go with B - Article. There are hundreds of good examples for the answer being B. For example, "a book" ('a' is an article - 'book' is a noun), "an apple" ('an' article - 'book' noun). Those are just the simple ones.
The greatest difference in magnifying power is between transmission electron microscopes and dissecting microscopes.
At first the people does not bluntly show gratitude to Jim, they treat what he does as his work which does not need gratitude. Later on, they learned that they must thank him for his work even if he gets paid for doing it. They should still show gratitude to him, this boosts his morale and will make him enjoy his work more.
