The Best Reason to Use a Mechanical Device, Such as an Actometer

The best reason to use a mechanical device, such as an actometer, is that

A) it permits the researcher to be free to measure other things in the study.
B) it is free from biases associated with human raters.
C) mechanical devices can assess a wide range of overt and covert behaviors.
D) it is easier to use with children than using questionnaires.