This is a controlled experiment. All variables are the same for each test tube except for the type of water.

It is impossible to conclude that the heat of the sun killed the plants and that their death was not due to the boiled water.

SInce both test tubes received the same amount of sunlight it is difficult to reach the conclusion that the heat, due to the sunlight, is responsible for the death of the plants.

Since this is a controlled experiment we can say that the evidence points to one variable and that is the boiled water. Further testing may be needed.

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