Living activities of cell require the stimulation of information objects. If one once loses the signalstimulus, cells lack the activities.
细胞生命活动需要信息物质的刺激，一旦失去信号刺激，细胞就缺乏生活力。
2
It predicts that the best timing is when the conditioned stimulus, which is the signal, comes before the unconditioned stimulus, which is what you have to prepare for.
它预测，最佳的时机，莫过于作为信号的条件刺激，出现在需要你做准备的，非条件刺激之前。
3
The researchers also tested the flies' saliva for enzymes that signal sleepiness and measured the flies' ability to associate a light with an unpleasant stimulus.