Which statement describes the validity of the student's results?
they are valid because the student ran a controlled experiment.
they are not valid because the student did not control all the variables that can affect plant growth
they are valid because the dependent variable caused a change in the independent variable.
they are not valid because the time frame to grow a plant is too short.

They are valid because the dependent variable caused a change in the independent variable.  

Option C

Explanation:

The validity of a student’s result is basically based on how the dependent variable caused a change in the independent variable. A dependent variable is one which a scientist produce a variable and finds means to explain it in a proper way. An independent variable is one that is formed to compliment the dependent variable.

When the independent variable increases it causes decrease or increase in dependent variable. A intermediate or intervening variable is found which helps explain about the changes happening between the Independent and interdependent variable.

Option (c) ''They are valid because the dependent variable caused a change in the independent variable'' is the correct answer.

Explanation:

The dependent variable is the one which is the center of observation. It is changed during the reaction and affected by it. When we measure the value of the reaction we always measure the dependent variable.

The independent variable is the one that is changed to cause the change in the value of the dependent variable. We can say that the dependent variable depends on independent for its reaction.

So dependent and independent variables are correlated with each other which tells the authenticity of the experiment.