维生素B1、维生素B2、维生素B6、维生素B12、维生素C、烟酸、叶酸是水溶性维生素。
参考答案：对
Was it two years ago _____ they first met? [ ]
A. since
B. which
C. while
D. that
In the data link layer, the data unit is called (71) ．
A．flame
B．Packet
C．Signal
D．APDU
