输血后感染HIV，这是经 A．医源性传播 B．垂直传播 C．食物传播 D．接触传播

爬行类从体形上显著区别于两栖类的特征是（）。

A、具有五趾型附肢

B、有尾

C、皮肤富有腺体

D、皮肤干燥，有角质鳞片或盾片，指趾端有爪

A security market with price continuity is most accurately characterized as a market in which:（）

A. assets can be bought or sold quickly with minimal transaction costs.

B. prices change rapidly from one transaction to the next in response to new information.

C. prices do not change much from one transaction to the next in the absence of new information.

领导群体结构

下列哪项是Rett综合征特征性的临床表现

A．绞手及洗涤样动作
B．言语性幻听
C．注意力不集中
D．喉咙发声
E．活动过度

为什么网络经济的到来会使边际效用递减的规律失效呢？