阅读课文中的语段，回答问题。

　　这种设计，在建桥史上是一个创举，既减轻了流水对桥身的冲击力，使桥不容易被大水冲毁，又减轻了桥身的重量，节省了石料。

1．这种设计指______________________的设计。

2．这种设计的优点，一是_____________，二是_____________。

TCP/IP （） layer protocols provide services to the application （） running on a computer. The application layer does not define the application itself, but rather it defines （） that applications need — like the ability to transfer a file in the case of HTTP. In short, the application layer provides an （） between software running on a computer and the network itself. The TCP/IP application layer includes a relatively large number of protocols, with HTTP being only one of those. The TCP/IP （） layer consists of two main protocol options — the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).

TCP/IP（）layer protocols provide services to the application.

A．application

B．transport

C．link

D．network