《单采血浆许可证》有效期满前（），单采血浆站应当向原发证部门申请延续，并提交相关材料。
A.1个月
B.2个月
C.3个月
D.6个月
参考答案：C
There was a fire in the street last night, but the firemen _______within twenty minutes. [ ]
A. took it out
B. brought it out
C. worked it out
D. put it out
刘星将一块重2N的橡皮泥放入水中后橡皮泥立即沉入水底；他取出橡皮泥将其捏成船状再放入水中，“泥船”却漂浮在水面上，他是利用了______方法来增大浮力的，此时“泥船”所受的浮力为______N．
