用葡聚糖凝胶SephadexLH-20分离下列黄酮，甲醇为洗脱剂，最先被洗脱的是（）
A.A
B.B
C.C
D.D
E.E
参考答案：B
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.
5（）
A．point
B．start
C．length
D．end
残疾
