[单项选择]We______ on it for many hours but we have not yet reached any concinsion.
A. work
B. have been worked
C. have been working
D. are working

[单项选择]We ______ on it for many hours but we have not yet reached any conclusion.
A. work
B. have been worked
C. have been working
D. are working

[单项选择]

Predictions of many robots in industry have yet come true. For ten years or more, manufacturers of big robots have explained how their machines can make industry mom competitive and productive. The maker for (21) robots is oversupplied now, and the driving force of the robotics(机器人学) revolution is (22) to be with makers of machines that handle a few kilos at most.
 "Heavy-robot manufacturers are in some difficulty (23) finding ustomer. They are offering big (24) just to get in the door. There has been a (25) growth everywhere in the numbers of robots, so we admit we are either deceiving (26) or that the market is slowly growing. "said John Reekie, chairman of Colen botics. "The following things must happen (27) the robotics revolution to occur. We must achieve widespread robot literacy(文化), (28) there has been a computer (29) program, there must be a robot prices. (30) , some kind o
A. to
B. for
C. in
D. with