Total color blindness usually occurs due to a genetic variation

The word "circadian" indicates that a circadian rhythm ________

a. is generated from within. b. occurs more frequently than once a day. c. occurs less frequently than once a day. d. is about 24 hours in length.

Research indicates that onset of puberty _______________

a. has remained relatively unchanged for several centuries b. is occurring at later ages than ever before in developed countries c. is occurring at earlier ages than ever before in developed countries d. is less important to teenagers today than it has been historically