单项选择题
A．have the light turned on B．be rewarded with milk C．please their parents D．be praised
A．would make learned responses when it saw the milk B．would carry out learned movements without being given milk C．would continue the simple movements without being given milk D．would turn its head to fight or left when it had enough to drink
A．the lights were directly related to some basic "drives" B．the sight of the lights was interesting C．they need not turn back to watch the lights D．they succeeded in "switching on" the lights