Answer:
The correct answer is (a), heating and soaking at a temperature above the austenitizing level followed by rapid cooling.
Explanation:
Tempering is a heat treatment that is performed to change microstructure of steel <em>and increase it's hardness.</em>
It is done by heating above the austenitizing level, because for this heat treatment it's necesary to heat the steel to get <em>austenite structure</em> that is the <em>alotropic form of gamma iron.</em>
The procedure of tempering, continues with rapid cooling, because this way you get the microstructure with the best hardness properties, that is <em>martensite.</em>
In an experiment there are three types of variables: Independent, dependent and constant variables.
The variable being tested and the parameters of which can be changed is the Independent variable. Here, the cleaning product is the independent variable.
Dependent variables are the ones which vary when change in the independent variable is made. How clean the counter is the dependent variable which is depending on the cleaning product (the independent variable).
Constant variables are the ones which are kept unchanged during the experiment so that it does not affects the result of the experiment. In the given experiment, the amount of cleaning product and the brand of the paper towel are the constant variables. Other constant variables can be the size of the paper towel, the technique of wiping, the temperature etc.
Shifting of tectonic plates.
Faults- two plates come together
Mountains- convergent movement
Islands- underwater volcanoes deposit volcanic rock into the same place until it's tall enough to be above sea level
C. Abraham Maslow, wrote a paper about these needs in 1943 called, "A Theory of Human Motivation.
