问答题 《复合题被拆开情况》 The atmometer (蒸发计) is the most simple and efficient instrument ever invented for the measurement of evaporation (蒸发量). Its readings are a measure of the combined effect of humidity(湿度), temperature, and wind, and are of great value in all kinds of agricultural and gardening operations. These operations require an estimation of differences in these factors that affect plant growth in different situations. Its installation requires only the use of a bottle and some tubes. The atmometer may also be used to maintain high humidity in experiments; to constantly provide moisture for the surface of growing plants. When buried in the soil and fed with water through tubes, the atmometer cup is capable of maintaining constant degrees of soil moistness being determined by the amount of water supplied above the soil. This type of atmometer cup was invented by Dr. Brown Livingston, Professor in Johns Hopkins University. Now we have three types of atmometers. Our prices for these types are: Natural cups— $ 5.00 per piece Coated at base— $ 6.00 per piece Coated and standardized— $ 11.00 per piece《问题》：Which type of the atmometer is the most expensive?