An independent variable is a. directly changed by the experimenter b. manipulated by changes to the dependent variable c. a variable that is kept constant d. a variable that is used as a control

A independent variable is a variable which the experimenter can control and by changing the independent variable the experimenter observes or records the value of dependent variable.

so i see if you are asking independent than the answer is A.

if you are asking dependent variable than the answer may be B because manipulated by changes to the independent variable would be the best answer.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs