One Shortcoming of Laboratory Observation Is That

One shortcoming of laboratory observation is that:

A) the presence of researchers and special equipment may cause subjects to act differently than they would in their natural surroundings.
B) some subjects are given detailed instructions about how to behave, whereas others receive only vague instructions.
C) the results often are inaccurate because many people have a distorted view of their own abilities and traits.
D) teachers and parents do not usually question the results from a laboratory observation since the results are summarized in a single, precise-sounding number.