Stress patterns may distinguish a compound word from a noun phrase consisting of the same component words. For example, a black board, adjective plus noun, is any board that is black, and has equal stress on both elements. When said in isolation, additional prosodic stress falls on the second word, but this disappears in the appropriate context. The compound blackboard, on the other hand, though it may have started out historically as black board, now is stressed on only the first element, black. Some dictionaries mark secondary stress on the second element, board.

【翻译】重音格式可以区分复合词和由相同单词组成的名词短语。例如a black board，是形容词加名词，指任何一块黑色的板子，在两个音素上都有相同的重音。当孤立被读的时候，重音则落在了第二个单词上，可是，此现象在适当的上下文中就会消失。另一方面，复合词blackbaord 虽然在以往的过去可能都是读black board，但现在只强调第一个音素，即black。有些词典在第二个音素board上面，标注次重音。

【分析】通过以上翻译，即可看出：

When said in isolation, additional prosodic stress falls on the second word, but this disappears in the appropriate context. 这句话，实际是在时间从句中省略了成分。

When said in isolation = When it is said in solation。it 指代下文的stress，said = read（读）

▲ 关于“从属连词 + 分词”这种结构，我用两种说法，来解释这个问题：

1. 为了让分词短语表达的状语意义更加明确，在之前加上适当的连词，例如，本句是时间状语，所以加了When。

2. 在某些状语从句中，当其主语跟主句的主语一致，而且含有be 动词时，可以把主语（一般是代词充当）以及be 动词一起省略。旨在使句子更加简洁和生动。

这个规则必须满足3个条件：（1）限于部分状语从句（2）主、从句的主语必须一致（3）有be 动词，这个be 动词可以是系动词，可以是进行时态的be，也可以是被动语态的be。