Prices fluctuate, in response to harvests, natural disasters and political instability; and when they rise, it takes some time before new sourcesofsupply become available.
价格会随着收成、自然灾害和政治不稳定而波动；当价格上涨时，需要一段时间才能找到新的供应来源。
2
They want to lock in sourcesofsupply.
他们想锁定矿石供应来源。
3
In recent years, corn ethanol has been one of the few sourcesofsupply growth in transport fuels.