听力原文:M: Have you seen Mr White? He usually comes here by 9:00.
W: He said he was coming at 9:30 today, but it's already 10:00. I wonder where he is.
When does Mr White usually arrive?
A.At 10,00.
B.At 9:30.
C.At 9:00.
D.At 8:30.
第2题
A、由正电胶体静电引力吸附
B、被负电胶体排斥,即负吸附
C、由不带电的胶体产生专性吸附
D、由于静电引力吸附,可使土壤胶体负电荷增加
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