Faun was so busy picking up its parcels that at first it did not reply.

picking up its parcels  这是动名词短语，然后busy修饰它吗？

【答】picking up its parcels是现在分词短语，作方式或伴随状语，修饰was so busy。

以下两种表达都正确：

Faun was so busy picking up its parcels that at first it did not reply. （picking up its parcels 是现在分词短语）

Faun was so busy in picking up its parcels that at first it did not reply. （picking up its parcels 是动名词短语）

▲ 现在分词可以作状语（表示方式、伴随等），“in+动名词”也可以用作状语（表示在哪一方面）。因此，有时在不改变句子意义的情况下，增添或减少介词便可以作为区分动名词和现在分词的标志。有介词是动名词；没有介词是现在分词。请比较：

Using his hybrid rice, farmers are producing harvests twice as large as before. 通过使用他的杂交稻种，农民现在生产的粮食是以前的两倍。（using是现在分词）

By Using his hybrid rice, farmers are producing harvests twice as large as before. （using是动名词）

They also express their feelings using unspoken language through keeping physical distance, actions or posture. 他们还通过使用无声语言，借助保持距离、动作和姿势，来表达感情。（using是现在分词）

They also express their feelings by using unspoken language through keeping physical distance, actions or posture.（using是动名词）

He must be able to use the foreign language, forgetting all about his own. 他一定要做到使用外语时，忘掉本族语。（forgetting是现在分词）

He must be able to use the foreign language through forgetting all about his own. （forgetting是动名词）

又如：

She caught cold by sitting on the grass.

She caught cold sitting on the grass.

她因坐在草地上面着了凉。

Mike wasn’t long in making up his mind.

Mike wasn’t long making up his mind.

迈克不久就会下定决心的。

I lost no time in talking.

I lost no time talking.

我一刻也没耽误地谈话。

They spent a lot of time in searching for the ways to solve the problem.

They spent a lot of time searching for the ways to solve the problem.

他们花了大量时间寻找解决问题的办法。

We are busy in making arrangement for Christmas. 

We are busy making arrangement for Christmas. 

我们正忙着做圣诞节的准备。

▲ 以上例句有介词时，“动词-ing形式”是动名词；无介词时，“动词-ing形式”是现在分词。