benefits of working for a non profit Ford motor co., in 1915, produced a car that was different from a horse model The response to single factor value is trend. The tendency is the selection bias produced by the stimulation of the organism on a single environmental factor, which is the directional response form of the organism to the external stimulus, including the two basic forms of orientation and avoidance. The tropism has the tendency of phototropism, thermal tendency, wetness, tendency, and oxygenicity. It has the avoidance of light, heat, moisture, anaerobic and so on. For example, the acidity of paramecium, the thermal tendency of bedbugs and the phototropism of insects. The trend is the common response of low biological cells, biological tissues and protozoa. Tropism is in a series of internal inductance organically combined in a certain direction, to form a structure of ordering, and external single environment factor to form a single reaction, the biological function between the body and the external environment on the coherent function, to accelerate the ordering of the body development. When this series of inductivity is combined in a positive way, the tendency is formed. When this series of induction is combined in reverse, it forms a negative trend - the avoidance. In summary, the trend is the most elementary preordinate response to the external things of single factor value. So why is yu 'e bao falling steadily?