Aresearcher is interested in the effects of nitrate and phosphate on plant growth and sets up an experiment in which
groups of five plants are given 1, 2, and 3 grams of nitrate and 1, 2, and 3 grams of phosphate in all combinations over
a period of one month. the researcher measures plant height and weight at the end of the experiment. what is missing
in this experimental design?
a) a control
b) an independent variable
c) a dependent variable
d) a constant

A control is that group in an experiment that does not receive any treatment and is used for comparison with the test result.

A) a control

Explanation:

In the experiment mentioned, the control is missing because the test group as mentioned are the plant set that receives the treatment that is the different concentration of nitrate and phosphate.

The effect of these nutrients on growth will be observed and evaluated. The time period of the experiment is one month which might exceed.

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explanation: