An artificial pacemaker is a device that regulates the beat of the heart by an electrical stimulus. Some early pacemakers were powered by batteries and were worn externally with wires passing through the skin to the surface of the heart. Modern pacemakers are now much smaller and are implanted surgically. Which most likely has increased the lifespan and effectiveness of artificial pacemakers?
A: the invention of lithium batteries

An organism, such as a nematode worm, may have only 1000 cells. It should be classified as being
A: multicellular.

A baby kit fox grows to become an adult with a mass of over 3.5 kg. What factor will have the greatest influence on this kit fox's survival?
A: the conditions of the fox's habitat

In humans, the amount of sugar in blood is controlled by the release of a hormone called insulin. This process is an example of
A:
regulation