The answer is an open system
Living components in a river ecosystem would include all plants, all animals, all microorganisms. Every fish species, every arthropod species, every reptile and amphibian species, all the birds, etc.
Answer:
I believe "B"
Explanation:
In the Sun, the flows of hot plasma in the convection zone create the solar magnetic field. This is sustained by nuclear fusion in the Sun. ... The number of sunspots on the sun increase and decrease over time in a regular, approximately 11-year cycle, which is, in fact the solar magnetic activity cycle.
Since the other answer got deleted, i'll just answer it for you.
a sinoatrial node is the main pacemaker that begins each heartbeat located in the junctions of superior vena cava and the right atrium. It signals from the node that spread through the atria and determines the heart rates.
