单项选择题
A．By making it work in such environments as deserts, oceans or space. B．By working hard for 10 or 20 years. C．By either properly programming it or changing its structure. D．By reproducing it.
A．are directly related to pleasure B．will meet their physical needs C．will bring them a feeling of success D．will satisfy their curiosity
A．if B．until C．that D．unless