In the 160 years in which "handedness" has been studied we have learned quite a lot, but we still cannot precisely describe what causes humans______to use one hand over the other, or why human populations are______toward right-hand use rather than left-hand use.

(A) The surplus generated by low-pressure systems can be sold, lessening overall water strain on a region.
(B) Low-pressure systems deliver water directly to root systems, resulting in higher crop yields.
(C) A lower cost is associated with low-pressure systems than with high-pressure systems, which are generally more expensive.
(D) Lower-pressure systems deliver water in such a way that evaporation rates are diminished, resulting in greater efficiency.
(E) Crops watered by lower-pressure systems generally contain higher nutrients, reducing overall food consumption levels.

(A) Researchers have not yet discovered a means of transporting photons more efficiently.
(B) Their primary limitation is the density of connections required between electronic microchip gates.
(C) Their accuracy level is poor at 8 to 11 bits, but still superior to that of electronic computers.
(D) They invariably rely on electronic circuits to preprocess input data for computation.
(E) Both analog and digital forms of optic computing are presently being developed by scientists.