The four limitations are
1.It's often impossible to repeat trials on the same subjects.
2-Subjects may report an inaccurate medical history.
3-It can be difficult to control all possible variables.
4-It's impossible to come up with testable scientific questions for human subjects.
Research involving human beings is ultimately necessary for improvements in human health and welfare. Any results about healthy physiology, illness causes, treatment effectiveness, learning, or behavior must be verified by carefully controlled investigations involving human participants. Sadly, not all human research have been valid and beneficial. It is possible to harm people in the name of research. The most well-known instances happened in Nazi Germany. Investigations conducted after the war found several crimes, including experiments in which participants were submerged in extremely cold water to determine how long it would take them to pass away from hypothermia.
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Answer:
The skeletal system is vital in supporting the immune system because : Bones contain marrow, a porous material which creates both white and red blood cells. This replenishment of cells allows the body to fight and expel harmful bacteria, environmental toxins, foreign material e.t.c.
The white blood cells formed by the marrow are instrumental in isolating and destroying harmful particles (either on the site or in lymph nodes), or transporting them to the kidneys or bowels for excretion.
NOTE : Some people have marrow disorders which prevent their marrow from forming new cells; this is caused most often by cancer. Today, it is possible to transplant marrow from a healthy individual to a sick patient, and so help their bone marrow form new white and red blood cells to fight their sickness.
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So here let's first find the amount of children every santa, in total, sees in one day. So if there are 400 santas, and each sees 125 children, you can just multiply 400 by 125 to see how many children all the Santas see in one day.
400 * 125 = 50,000
Now, since there are 30 days which all the santas see 50,000 children, you can then multiply 30 by the 50,000 children to get how many children are seen by Macy's Santas in a month.
30 * 50,000 = 1,500,000
So 1,500,000 children are seen by Macy's Santas.
One of the 4 layers that surrounds the earth.
When the two atoms are split
