地下水按其存在状态不同，可分为（）、（）和（）三种类型，其中以（）最为重要；按其存在

关于支气管扩张主要累及的部位以下哪种描述是正确的（）

A.直径>2mm中等大小的近端支气管

B.直径<2mm细小的远端支气管

C.直径>5mm中等大小的近端支气管

D.直径<5mm细小的远端支气管

E.直径>10mm中等大小的近端支气管

下列关于酸枣仁对中枢神经系统的作用，错误的是（）

A.镇静催眠

B.安定

C.抗惊厥

D.镇痛

E.兴奋

一般而言，客户年龄越大，所能够承受的投资风险越高。( )

IP multicasting is a set of technologies that enable efficient delivery of data to many locations on a network. Rather than making multiple copies of a message intended to be distributed to multiple recipients at the (71) of origin of a message, multicasting initially sends just one (72) and does not copy it to the individual recipients until it reaches the closest common point on the network, thereby (73) the bandwidth consumed. Network performance is significantly (74) because it isn’t bogged down with the processing and transmission of several large data fries; each receiving computer doesn’t have to (75) the transmitting server for the file.

A．point

B．bottom

C．head

D．sight

简述强制对流，自然对流的含义。