The presentation layer is concerned with the（1） and semantics of the information exchanged between two systems. The processes in two systems are usually exchanginginformation in the form of character（2）numbers, and so on. The information should bechanged to bit （3） before being transmitted. Because different encoding systems, thepresentation layer is responsible for （4）between these different encoding methods. Thepresentation layer at the sender changes the information from its sender-dependent format into acommon format. The presentation layer at the receiving machine changes the common format intoits （5） dependent format.

（2）是（）

A.numbers

B.functions

C.strings

D.codes

影响飞机的纵向稳定的主要因素有（）.

A、垂直尾翼

B、水平尾翼

C、后掠角和上反角

D、重心