With age, muscles can become weaker. this is due to a. connections between nerves, which cause more pain and therefore less use b. damage from everyday use and injuries that accumulate over time c. disconnections between motor nerves and muscle fibers d. difficulties that occur during muscle growth and repair

Explanation:

Motor nerves are located in the central nervous system, their function is to send signals from the central system to muscles, which are formed by fibers. (see image attached).

Therefore, if there's no connections between motor nerves and muscle fibers, there won't be any movement, because nerve signals send the information needed to cause movements. So, if the muscle don't move, it will become weaker, decreasing its strength and size.

to prevent people from getting the ebola virus, countries around the world paid to doctors develop a new vaccine. now that the vaccine has been made, doctors will need to experiment on a large number of people to find out if it works safely.

what is the greatest limitation that scientists are dealing with as they try to figure out how to experiment with the ebola vaccine?

meditation is a practice of sitting still and quiet for minutes or even hours. it has been practiced for thousands of years and is even a part of religious practices for some people. carefully controlled, repeated measurements of brain activity have shown that meditation does increase certain chemicals in the brain and even grows the part of the brain that people connect with their current surroundings and activities.

are claims about the effects of meditation most likely scientific or pseudoscientific?

not pseudoscientific, because people have made claims about it but scientific observations have not been made