The correct answer is: A. each part
The banana tree is a very versatile plant, and every part of it can be used by humans. The fruit is eaten fresh or cooked, the leaves are used to make food wraps, the trunk is used to make furniture, and the fibers from the leaves are used to make rope.
Option B, "any part," is incorrect because not all parts of the banana tree are used by humans. For example, the roots are not edible.
Option C, "most part," is incorrect because all parts of the banana tree are used by humans.
Option D, "No improvement," is incorrect because the sentence is grammatically correct and does not need to be improved.