Research into the Development of Sexual Orientation

Research into the development of sexual orientation . . . ​

A) is relatively easier to conduct than research into other variations in human behavior.
B) is assisted by the fact that the large majority of researchers define the categories of sexual orientation in a consistent manner.
C) may overestimate the differences between people of various sexual orientations because people who do not fit neatly into one category or the other may not be included in research samples.
D) has been very consistent with regards to biological causes.