求问分词修饰到底要不要加逗号？！

lfchun521

In the mid-1920s the Hawthorne Works of the Western Electric Company was the scene of an intensive series of experiments that would investigate changes in working conditions as to their effects on workers' performance.
A. that would investigate changes in working conditions as to their effects on workers' performance
B. investigating the effects that changes in working conditions would have on workers' performance  
C. for investigating what the effects on workers' performance are that changes in working conditions would cause  
D. that investigated changes in working conditions' effects on workers' performance
E. to investigate what the effects changes in working conditions would have on workers' performance

答案是B
我不明白的是investigating在这里是作为现在分词修饰experiments，但是之前在OG里看到说分词修饰前必须加逗号，所以就疑惑了
问各位大牛，分词修饰前的逗号到底必不必须啊？？

ai559031

沒有規定分詞片語一定要有逗號，有逗號的是非限定
沒逗號的就是限定修飾，通常做形容詞修飾主詞或受詞
舉例： a judge overturned the ban on the ground that it violated state laws allowing the use of personal watercraft on common waterways.
此句做形容詞

lfchun521

ai559031 发表于 2016-7-19 21:17
沒有規定分詞片語一定要有逗號，有逗號的是非限定
沒逗號的就是限定修飾，通常做形容詞修飾主詞或受詞
舉例 ...

哦哦，明白了，谢谢！！