Every instance of an abstract type is an instance of some concrete subtype.

SUBTYPE定义的数据类型是原类型的一个子集，仍属原类型。

Which subtype of Bipolar Disorder is more likely to be associated with Anxiety Disorder? （ ） A: Biphasic type I disorder B: biphasic type II disorder C: circular mood disorder D: unconformity of biphasic disorder

下面关于IEEE 802.11 MAC帧一般格式说法正确的是（） A: Frame Control 字段所有帧的开头均是3个字节的帧控制位 B: Protocol位协议版本为由4个比特构成 C: Type与subtype有3种帧类型 D: 数据帧负责在服务器之间传输数据

若W2、L已经定义，并且N2BIT、  ARRAY_N2BIT、P的有关定义如下： SUBTYPE N2BIT IS STD_LOGIC_VECTOR(W2-1 DOWNTO 0);   TYPE ARRAY_N2BIT IS ARRAY (0 TO L-1) OF N2BIT;   SIGNAL  P: ARRAY_N2BIT;        则信号P综合成硬件后相当于一个存储器/寄存器组，该存储器/寄存器组具有L个存储/寄存单元，每个单元具有W2位数据。

Which<br/>one of the following is the reason of pandemic<br/>flu<br/>() A: virus<br/>has strong virulence <br/>(B)HA<br/>of Influenza B: virus<br/>easily produce variation, and people lack of immunity <br/>(C)<br/>NA of Influenza C: virus<br/>easily produces variation, and people lack of immunity<br/>(D)<br/>Influenza D: virus<br/>develops new subtype virus, and people lack of immunity