Why are experimental investigations the best type of scientific investigation to demonstrate cause-and-effect relationships?

Experimental investigations are the best type of scientific investigation to demonstrate cause-and-effect relationships because they allow the investigator to actively manipulate variables and control conditions.The independent variable can be isolated and manipulated,producing a change (or no change) in the dependent variable.This change can be measured to gather evidence to support or refute the cause-and-effect relationship.

b) the planets year length would be longer

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answer; /// i do believe the correct answer is ( a