_______________, the basic units of heredity, are located on chromosomes

It is difficult to distinguish between colors at night because __________

a) we are seeing primarily with the cones. b) rods do not adapt to the dark. c) we are seeing primarily with the rods. d) we are used to seeing mostly with the fovea.

To eliminate sources of error in drug research, the researchers use ______ in their research

a. convicted drug dealers c. the case-study approach b. the double-blind procedure d. synthetic imitations of real drugs