未知题型 Essay-type Questions What are the characteristics of MSS, TM and ETM+ images? Please analyze the spectral features of the TM bands and explain the principle of the vegetation index calculation, and try to illustrate the application of the vegetation index.

单项选择题 中国居民平均每天钙的摄入量，与营养学会推荐量（RNI）相比，每天居民钙的差距约为（）

单项选择题 对于维生素D的概括错误的是（）