俗话说：“人往高处走，水往低处流。”水总是从高处流向低处是因为水受到 力的作用，这个力的方向是 。
重 竖直向下
At a basic level, cloud computing is simply a means of delivering IT resources as (1) . Almost all IT resources can be delivered as a cloud service: applications,compute power, storage capacity, networking, programming tools, even communication services and collaboration (2).
Cloud computing began as large-scale Internet Service providers such as Google,Amazon,and others built out their infrastructure. An architecture emerged: massively scaled, (3) distributed system resources, abstracted as virtual IT services and managed as continuously configured, pooled resources. In this architecture, the data is mostly resident on (4) "somewhere on the Internet" and the application runs on both the "cloud servers" and the user's browser.
Both clouds and grids are built to scale horizontally very efficiently. Both are built to withstand failures of (5)elements or nodes. Both are charged on a per-use basis. But while grids typically process batch jobs, with a defined start and end point, cloud Service can be continuous. What's more, clouds expand the types of resources available file storage, databases, and Web Service and extend the applicability to Web and enterprise applications.
空白（5）处应选择（）
A.entire
B.individual
C.general
D.separate
能与甾体皂苷生成难溶的分子复合物的甾醇类化合物，其必需的结构特点是（）
A．3β-OH，A/B环反式稠和
B．3α-OH，△3的结构
C．3α-OH，A/B环反式稠和
D．3α-OH，A/B环顺式稠和
E．3β-O-糖基
