单词	賣買人爲低品
释义	同CLASS
随便看	observational frequency observational learning observationally observationally equivalent observational method observational network observational point observational research observational site selection observational skill observational statement observational study observational twilight observation and learning activities observation angle observation angle (of a retroreflector) observation angle [of a retroreflector] observation apparatus observation aviation observation balloon observation battalion observation board observation boat observation buoy system observation car