What are the four main ancestors of horses?

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Many organizations release indexes used to measure the development of the world's countries. as we learned in this lesson, these indexes measure many factors, from life expectancy to happiness. in your opinion, what are the three most important factors we can use to determine how developed a country might be? explain your answers in a few sentences.

Compare the parts of a cell and the cell as a whole to another common nonliving system (i.e., a car, a city, describe the parts of a cell and their primary function.