What distinguishes an experiment from a scientific investigation?

• A. An experiment tests a hypothesis under controlled conditions, while a scientific investigation may involve observation and data collection without manipulation.
• B. A scientific investigation always uses experiments.
• C. An experiment is the practice of observation without any data collection.
• D. Both terms refer to the same process.

Answer: (A)

The main idea here is the difference between testing ideas by actively manipulating conditions and gathering information through observation. An experiment is about testing a hypothesis by changing one factor (the variable you deliberately alter) while keeping everything else as constant as possible, so you can see the effect of that change under controlled conditions. A scientific investigation, meanwhile, covers any rigorous inquiry into natural phenomena and can include observing, measuring, and collecting data without manipulating variables at all.

That’s why the best choice says an experiment tests a hypothesis under controlled conditions, while a scientific investigation may involve observation and data collection without manipulation. For example, changing the amount of nutrient in plant soil and measuring growth is an experiment. Observing animal behavior in its natural habitat or analyzing existing data to find patterns is a scientific investigation that may not involve manipulating anything.

The other options don’t fit because they imply that all investigations are experiments, or that experiments involve only observation without data collection, or that both terms mean the same process.