跟单员跟踪原材料主要是监督供应商是否已经按要求备齐原材料。( )
参考答案:对
Not until the early years of the 19th century ________ what heat was.
A.man did know
B.did man knew
C.didn't man know
D.did man know
滴眼剂中加入下列物质其作用是
甲基纤维素()
A.调节渗透压
B.调节pH值
C.调节粘度
D.抑菌防腐
E.稳定