Task：The differences in wheat exports over three different areas.
1. 分段原则为： 每条线一段，即上升的一段，下降的一段，波动的一段。
3. 注意一类数据的描述(Max, Min，起点，终点，交点)。
The three graphs of wheat exports each show a quite different pattern between 1985 and 1990. Exports from Australia declined over the five-year period, while the Canadian market fluctuated considerably, and the European Community showed an increase.
In 1985, Australia exported about 15 millions of tonnes of wheat and the following year the number increased by one million tonnes to 16 million. After that, however, there was a gradual decline until 1989 and 1990 when it remained stable at about 11 million tonnes.
Over the same period, the amount of Canadian exports varied greatly. It started at 19 million tonnes in 1985, reached a peak in 1988 of 24 million, dropped dramatically in 1989 to 14 million tonnes and then climbed back to 19 million in 1990.
Seventeen million tonnes were exported from the European Community in 1985, but this decreased to 14 million tonnes in 1986 and then rose to 15 million in 1987 and 1988 before increasing once more to 20 million in 1990.