1、单选题：
GDPexcludesmostitemsthatareproducedandsoldillegallyandmostitemsthatareproducedandconsumedathomebecause
选项：
A:thequalityoftheseitemsisnothighenoughtocontributevaluetoGDP.
B:measuringthemissodifficult.
C:thegovernmentwantstodiscouragetheproductionandconsumptionoftheseitems.
D:theseitemsarenotreportedonincometaxforms.
答案: 【measuringthemissodifficult.】