A student is conducting their science experiment on the effect of caffeine on dogs. He has 3 groups of test subjects. The 1st group of dogs receives plain water. The 2nd group of dogs receives 10 mg
of caffeine each, and the 3rd group receives 50 mg of caffeine each. He will measure their activity
levels by recording how long each dog runs without stopping, after giving them the pills. What is the
control group in this experiment?
A. How the caffeine is given to the dogs.
B. The dogs that receive water.
C. The dogs that receive 10 mg of caffeine.
D. How the activity levels are measured.

The control group might be defined as the one that does not receive any treatment -meaning the independent variable-. So in this example, the control group are the dogs that receive water (option B). These dogs do not get caffein, which is the independent variable.

During an experiment the researcher compares at least two groups: a control group and an experimental group. Both groups are composed of individuals coming from the same population, so they are identical in all aspects except for the independent variables.

So, in the exposed example, the population is composed of dogs. From this population, the researcher selects one control group and two experimental groups. The independent variable in this study is the amount of caffeine provided to dogs.

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c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.