如前所述，最常出现的问题是缺少某些先决条件。
As mentioned above, the most frequent obstacle encountered is missing prerequisites.
先决条件(俗称“受的”)的人卖东西，必须完成或安排之前，买方可以购买，或许在某些情况下，卖方可以。
Conditions precedent (commonly called "subject to's") are those things that must be done or arranged before the buyer can buy or, perhaps in some instances, the seller can sell.
论述了实现这设想的先决条件为：所监测的变量必须是实测的、空间连续的、时间连续的和快速响应的，并介绍了为此所开拓的某些方法。
The prerequisites for this idea are that variables to be monitored must be measured, space-continuous, time-continuous and fast responding ones concurrently. To meet them, some methods are developed.
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