很简单
我们说take part in -- - ,但如果有形容词修饰part的时候,我们就要加一个a / an,如：take an active part in- ----又如：
1 Taiwan is part of China,但Taiwan is an indispensable part of China
2 This is part of my money for you.但：This is only a small part of my money for you.
( 明白了吗?good day to you)语感告诉我，没有这样的用法。同样的道理还有：have lunch, have a big lunch,He ate (a) half of the cake, He ate a big half of the cake.做个有心人，你就会学得更多。你我的语感应该不是一个概念。我是做英语工作的。请问，你是什么职业？