What is the difference between an open and closed circulatory system?

Elephants in the savanna regions of africa dig holes in dried up river beds to reach water lying just below the surface. these holes provide drinking water for other animals as well. so, without the elephants, many animals might otherwise die from lack of water during the dry season. the location in which the elephants live is an example of a/n and the role they play in creating water holes is an example of a a) ecosystem; habitat b) community; niche c) habitat; niche d) niche; habitat

What organs comprise the respiratory system of a bird

How can we use spectral lines of light coming from the superclusters to identify which is receding from earth at the slowest rate.