下列哪些维生素经皮肤易于吸收（）。

A.维生素A

B.维生素E

C.维生素C

D.维生素B

A socket is basically an end point of a communication link between two applications. Sockets that extend over a network connect two or more applications running oncomputers attached to the network. A sockettwo addresses:. Sockets provide acommunication channel between one or more systems.
There aresockets separately using TCP and UDP.

A．message and packet

B．packet and frame

C．stream and datagram

D．flow and block