For example, as for the food prices, the general rule is that the price is low in fall and high in spring.
比如就粮价而言，一般的规律是秋季粮食价格低，春季粮食价格高。
RULE 3. Sell when prices decline below old top levels or high prices.
规则三：当价格下降到历史顶部或高位以下时卖出。
RULE 1. Buy at new high prices or old top levels.
规则一：在新高位或者历史顶部买入。
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