What is the simple subject of the following sentence "a virus is a microscopic organism."

Walking is not the most exciting form of exercise a person can take on for fitness. yet it is low impact and requires no fancy equipment. that makes walking a simple activity for those new to exercise. walking is less likely than other exercises to cause injury to leg tendons and muscles. all it requires is a good pair of sneakers-no cables, stylish outfits, or weights required. of course, a person could increase the benefit of a workout by adding weights or speed walking. identify the main idea of this paragraph. walking is a difficult and safe exercise for beginners. walking is an easy and safe exercise for beginners. walking is a boring and dangerous form of exercise. walking is an exciting and very effective form of exercise.

Which word in this excerpt from act i, scene i, of richard iii means “to listen”

The vast muslim world was wonderful for the growth of knowledge. the greeks had developed a level of practical experience and technical understanding a thousand years more advanced than anyone else nearby. the muslims began to translate some of these ancient greek texts. from india, muslims learned of the zero, which allowed them to invent what we still call "arabic” numerals. and because the koran, the sacred book of islam, is written in arabic, scholars throughout the muslim world learned to read arabic and to share their knowledge. the muslims swept past jundi shapur and learned the secrets of sugar. as they conquered lands around the mediterranean sea, they spread word of how to grow, mill, and refine the sweet reed. how do the details in the passage support the central idea? the details describe the important role muslims played in spreading knowledge throughout the world. the details clarify the role jundi shapur played in spreading the secrets of sugar to the rest of the world. the details describe how muslims used knowledge from only the greeks to make innovations. the details reveal how important the koran was in muslims conquer other lands