Which of the following statements about biological sex is FALSE?

A) No one characteristic defines sex.
B) Sex involves a cluster of biological attributes.
C) Sex is fixed at conception.
D) Sex develops gradually during prenatal development.

Biological sex is not strictly fixed at conception, as hormones and other biological factors can influence the development of sex characteristics throughout prenatal and postnatal development. Additionally, intersex individuals may have chromosomal or anatomical differences that do not fit typical male or female categories.