Look at the following three statements about internal and external validity:

1. Internal validity is high when we can be sure that changes in the dependent variable were produced by changes in the manipulated variable, and not by extraneous variables.
2. One way to assess external validity is to ask yourself if the obtained results can be useful in the "real world".
3. Internal validity is high when valid generalizations to a larger population can be made.

Which of the statements are correct?

Select one:

A.I. is correct.

B.I. and II. are correct.

C.I. and III. are correct.

D.All the above answers are correct.