若函数$\sin \alpha -\cos \alpha =-\frac{1}{3}(0<\alpha <\frac{\mathrm{\pi }}{2})$，则$\alpha$属于（　　）．

下列四本书中，记载“甘薯所在，居民便有半年之粮，民间渐次广种”一语的，只能

下列古诗句中描述的声现象是由空气的振动所产生的是（    ）    

The hospital in Harbin is already _________ of shocking mistreatment, as a 74-year-old man died of heart failure, after 67 days of treatment which cost the family 5.5 million yuan.   

有机物F 是一种新型涂料固化剂，可由下列路线合成（部分反应条件略去）．

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