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:EVERY OBJECT REMAIN AT THE STATE OF REST IN A UNIFORM MOTION UNLESS AN EXTERNAL FORCE ACTED UPON IT
Explanation:
Natural selection can only occur because of a variety in a population. Natural selection refers to environmental factors that affect a population and causes some of the population to have more surviving offspring than others. An example is a giraffe with a longer neck will be more likely to survive and reproduce (as it can gather more food from taller trees)
Answer:
2.
Explanation:
The movement of sediments from water (rivers) and wind (air) is basically what erosion is.
Answer:
d. xylem and phloem
Explanation: plants possess vascular bundles.these are bundles which includes xylem and phloem tissues and transport useful substances to various plant cells.
New Xylem and phloem are formed from the vascular cambium which divides into new cells .
Xylem and phloem are thin and slender with pipe-like structure.
The xylem transports water and dissolved nutrients to the cells where they are needed.
The phloem transports the product of photosynthesis (sugar) to parts what they are used up or stored .
Xylem cells are dead and consists in vessels,trachieds and xylem parenchyma.
Phloem cells are dead and consists in sieves cell, companion cells, phloem parenchyma and phloem fibres.
