正常成人的尿比重为（） A.1.010～1.020 B.1.101～1.015 C.

— Is there any better way to help my son get rid of the habit of playing computer games?

— To tell you the truth, it's very hard. But we      on this problem to improve the situation.[      ]

A. were working

B. had worked

C. are working

D. had been working

Would you mind if I sit here?

~  , It’s for Miss Zhou.

A. Better not   B. Never mind   C. Of course not

如图所示装置（气密性良好），若先将甲中液体挤出，观察到气球明显鼓起，一段时间后恢复原状；再将乙中液体挤出，气球又明显鼓起。下列组合正确的是

未列入麻醉品管理范围的镇痛药是（）。

A.哌替啶

B.美沙酮

C.芬太尼

D.纳洛酮

E.喷他佐辛

500kV及以上并联电抗器的中性点电抗器出厂试验应进行（）。