甘油明胶
A.硬脂醇220gB.十二烷基硫酸钠15gC.白凡士林250gD.羟苯乙酯0.25gE.丙二醇120g水加至1000g
参考答案:D
Packet-switching wireless networks are preferable (1) when transmissions are (2) because of the way charges are (3) per packet. Circuit-switched networks are preferable for transferring large files or for other lengthy transmissions because customers are (4) for the (5) of time they use the network.
4()
A.charged
B.fined
C.free
D.controlled
直流牵引电动机为什么采取串励的形式?