Line graphs that indicate time along the x-axis can be used to predict what would happen to dependent variables in an experiment at a later point in time
a only if the existing line shows an upward trend.
b only if the existing line shows a downward trend.
c if a new variable was introduced to the experiment.
d if the experiment continued under the same conditions.

The correct answer would be d if the experiment continued under the same conditions.

In any experiment, it is very important that all the physical conditions (such as temperature, pH, living environment if living tissue or organism in used in the experiment et cetera) must remain the same throughout the experiment.

In addition, if the experiment is repeated to check the reproduciblity, then also all these constant variables or conditions must remain the same.

It helps in getting accurate results as well as in reproducing the same results.

The upward or downward trend in a graph is a part of the result we obtained after the experiment.

D

Explanation:

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