在晴天下午，密闭的玻璃温室中栽培的玉米，即使温度及水分条件适宜，光合速率仍然较低，其主要原因是[ ]

A．O₂浓度过低

B．O₂浓度过高

C．CO₂浓度过低

D．CO₂浓度过高

While most recent attention in the AI field has been focused on expert system software, AI (66) has also seen dramatic advances. Activity in the past years was characterized by new low-cost, powerful Lisp machines, the introduction of AI workstations, Lisp compilers becoming available for all major professional and engineering workstations, and the personal computer emerging as a (67) . tool for expert system development. The next few years will see this technology evolves further.
Because the (68) of an AI computer represents a sizable investment, companies should carefully (69) all options that are available as well as have a good idea of what the next generation of systems will offer in order to (70) the optimum system. This publication provides the information necessary to gain this understanding.

A．choice

B．read

C．important

D．software

E．hardware

F．significant

G．emergence

H．survey

I．purchase

J．select