There are many ________ on the street.[ ]
A. people
B. peoples
C. people's
D. peoples'
答案:A
如图,可见腹主动脉及其分支纵切超声图,图中与腹主动脉平行的分支为_______。
若水样颜色深、浑浊且悬浮物多,用亚甲基蓝分光光度法测定硫化物时应选用何种预处理方法?