题目

Silk ___________ one of the primary goods traded along the Silk Road by about 100 BC. A . had become B . was becoming C . has become D . is becoming 答案：A 下列电离方程式错误的是 [　　] A． NaHCO3Na+＋H+＋CO32－ B． NaHSO4Na+＋H+＋SO42－ C． H2SO42H+＋SO42－ D． KOHK+＋OH－