原级：trough
1. China's national economy has seen three peaks and troughs since 1990, each of which brought about major policy adjustments to ensure smooth economic growth.
2. They dug ditches and built troughs to draw water from springs for daily use and irrigation.
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3. It marked the peaks for some, and the troughs for others.
4. Both indexes have risen about 40 percent and 70 percent respectively off their March troughs as investors bet on a speedy economic recovery.