若函数f（2x+1）=x2-2x，则f（3）=（ ）。

Directions: Read the following text and choose the most suitable heading from A—F for each paragraph. There is one extra heading which you do not need.

A.  Forecasting Research B.  Well-known Weather Forecasters C.  Severe Weather Events D.  Weather Forecasting E.  The Forecasting Process F.  Historical Background

小题1:
The task of predicting the weather that will be observed at a future time is called weather forecasting.  As one of the primary objectives of the science of meteorology, weather forecasting has depended critically on the scientific and technological advances in meteorology that have taken place since the latter half of the 19^th century.
小题2:
Throughout most of history, forecasting efforts at any given site depended solely on observations that could be made at the site.  With the development of the telegraph in the mid-1800s, weather forecasters were able to obtain observations from many distant locations within a few hours of the collection of such data.  Weather forecasting was revolutionized in the 1920s by the work of a group of Norwegian scientists.  This group provided a consistent and empirically based description of atmospheric circulation systems.  Current weather-forecasting techniques were initiated by the theoretical work of American meteorologist Jule Charney in developing numerical weather prediction.  Experimental numerical forecasts in 1950 proved so fruitful that they were soon adopted on a practical basis.  Since then, computerized systems based on numerical models have become a central part of weather forecasting.
小题3:
The process of making a weather forecast can be separated into three steps: observation and analysis, extrapolation to find the future state of the atmosphere, and prediction of particular variables.  The standard extrapolation technique is to assume that weather features will continue to move as they have been moving.  In some cases the third step simply consists of noting the results of extrapolation, but actual prediction usually involves considerable efforts beyond this. 
小题4:
Great attention is paid to weather forecasts during times of severe events (blizzard, hurricane and typhoon, tornado), and so forth.  Accordingly, the National Weather Service (NWS) commits significant resources to the forecast of such events.  Blizzards or strong extra-tropical cycles are handled through the usual forecast information channels, with the local NWS office issuing special advisories as appropriate.
小题5:
A number of new observing systems are being developed for forecasting purposes.  These include the Next-Generation Radar digital weather radar, which is intended to detect motions towards or away from the radar installation.  In addition, automated systems are being developed for taking observations at surface stations and on board buoys, ships, and aircraft.  The communications, processing, and display systems intended to govern this torrent of further data are still being elaborated.