在浮选生产实践中，下述哪种药剂一般不宜采用分段添加（）。
A、硫化钠
B、黄药
C、亚硫酸盐
D、石灰
参考答案：D
注册商标的有效期为（ ）年，自核准注册之日起计算
A．五
B．八
C．十
D．十二
A．No alcohol is allowed in the hospital.
B．No smoking is allowed in the hospital.
C．The patient should wake up at 6:30 in the morning.
D．Only two people are allowed to visit the patient at one time.
