What types of laboratory experiments are most desirable?

What types of laboratory experiments are most desirable?
 a. When the sample is representative of the population to which the results are generalized.
  b. When the experiment's context and conduct are natural so that the subjects behave realistically.
  c. When the intent of the experiment is to achieve high levels of internal validity.
  d. When the intent of the experiment is to achieve high levels of external validity.
  e. None of the above are desirable.

Question 2

In an experiment, which type of outcome variable(s) does a researcher have NO control and NO ability to manipulate?
 a. Dependent variables
  b. Independent variables
  c. Extraneous variables
  d. Both the independent and dependent variables.
  e. All of the above.