What is always included in a comparative investigation?

a. a dependent variable
b. an independent variable
c. a hypothesis
d. a scientific question

The options that can be included in comparative investigation  from the question is scientific question.Comparative Investigation can be regarded as one of the investigation that  Involve collection of  data on different populations as well as organisms, using different conditions  this condition could be Times of year or  locations so as to make a good comparison. Example of comparative investigation is identification of  the boiling points of three  liquids that are different, another one is making use of a hand lens when observing  the external anatomy of two different insects Things that should be included in comparative investigation are stated below Observations. QuestionData, GraphsConclusion.

Therefore, option A is the correct answer.

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The teacher is mostly talking about the distillation of a mixture