渣中Al2O3含量增加时对渣的粘度的影响是:()。
A.增加
B.降低
C.视情形不同既可降低亦可增加
参考答案:A
I ________ be quite bored with the job, but now I have________ to it.
A.used to; been used
B.used to; used
C.was used to; got used
D.was used to; been used
简述发光二极管的工作原理?