(51) is a six bytes OSI layer 2 address which is burned into every networking device that provides its unique identity for point to point communication.
(52) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.
(53) functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.
(54) is the popular LAN developed under the direction of the IEEE802.5.
(55) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.

A．X.25

B．ATM

C．FDDI

D．SMDS

称取一元弱酸HA1.04g，配制成100.0ml，测得其PH=2.64，计算该一元弱酸的PKa的近似值。（HA的摩尔质量M=122.1g/mol）