When would a scientist choose to conduct a controlled experiment

In which research method does a researcher change the value of one variable to determine how the change affects another variable? a. experiment b. observational research c. survey d. case study

Which best expresses the radical republican philosophy of reconstruction? a. the confederate states were conquered territories that should be ruled by military governors. b. the southern states actually never left the union. c. if ten percent of the voters of a state that had seceded took an oath of allegiance to the union, then it should be readmitted as a state.

Which social media guideline defines what to do if you find a fabrication on a social media site?