Eliza Takes Care to Illustrate in Her Research Report How

Eliza takes care to illustrate in her research report how long she was in the field and how she has minimized observer effects.
-LuAnn, a child development researcher, recently conducted a study in a hospital nursery to examine the feeding habits of newborn babies. She did not tell parents her identity or the purpose of her work when she asked them questions. This concern with LuAnn's study is most directly related to a concern with

A) external validity.
B) internal validity.
C) reliability.
D) ethical concerns.