Answer:
D. Test a piece of treated iron and a piece of untreated iron under the same conditions.
Explanation:
A controlled experiment is defined as an experiment where the experimenter or the researcher tries to test or experiment his result by changing one variable at a time and keeping the other factors under the same conditions and sees how it effects the result.
The factors which can be changed in an experiment is called its variables.
In the context, testing a piece of treated iron as well as a untreated piece of iron under the same working conditions forms a controlled experiment.
Answer:
The neuron is the basic working unit of the brain, a specialized cell designed to transmit information to other nerve cells, muscle, or gland cells. Neurons are cells within the nervous system that transmit information to other nerve cells, muscle, or gland cells. Most neurons have a cell body, an axon, and dendrites.
Explanation:
The frequency of an organ pipe if it is open is given by :

v is speed of sound in air is 343 m/s at 20°C
For fundamental frequency, n = 1

First overtone frequency,

Second overtone frequency,

Third overtone frequency

Hence, this is the required solution.
The type of graph that would most appropriately display Sarah's data is a line graph.
<h3>What is a line graph?</h3>
A line graph, sometimes referred to as a line plot or a line chart, is a graph in which individual data points are connected by lines. A line graph shows numerical values over a predetermined period of time.
Line graphs are frequently used in finance to show the historical price movement of an asset or instrument. To monitor changes over both short and long time periods, line graphs are utilized. Line graphs can be used to compare changes for multiple groups over the same time period.
In this case, it should be noted that Sarah wants to compare the speed and the height. Therefore, the line graph and s appropriate.
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It accelerates in the y component (bc of gravity) AND the x-component (b/c of the friction force).