题目

It is _____ work of literature that many people are desperate to have a copy of it. A. so unusual a    B. such unusual   C. so unusual    D. such unusual a 答案：A只用一种试剂，可区别Na2SO4、AlCl3、NH4Cl、MgSO4四种溶液，这种试剂是（  ）A．HCl B．BaCl2C．NaOHD．AgNO3