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On the results of measuring the amount of plastic found in a sample of 31
fish:

> その結果、９匹の体の中から大きさ **が** ５ｍｍ以下のプラスチック **が** 平均で１．１個見つかりました。  
>  The result (was that) from 9 fish the size was at least 5mm of plastic but
> on average they found 1.1mm.

I'm struggling with several aspects of the grammar in this sentence:

1) Is the first が in bold a subject marker and the second が the conjunctive
particle? Is there a だった omitted before this が?

2) Is the counter word 個 somehow used as a substitute for repeating the unit
mm?

If not, then I'm lost on how to parse this sentence.
CC BY-SA 4.0
2017-03-12T17:11:33.957
44345
2019-12-08T05:13:44.023
2019-12-08T05:13:44.023
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question
grammar particle-が counters
Can だ/だった be omitted before conjunctive が?
Both が in this sentence are subject markers.

Consider this "double-subject" sentence (cf. 象は鼻が長い / 私は彼が好きだ):

> そのプラスチックは大きさが5mm以下だ。  
>  Those plastic (fragments) are 5 mm or smaller in size.

Form a relative clause from this (note that ～以下 works as a no-adjective):

> 大きさが5mm以下のプラスチック  
>  the plastic (fragments) which are 5 mm or smaller in size

With this as the subject of the main sentence, you can say:

> 大きさが5mm以下のプラスチックが見つかりました。  
>  The plastic (fragments) which were 5 mm or smaller in size were found.

個 is a generic counter for small and round objects. 個 is not a pronoun and it
never replaces a unit of length, time, etc. So this 1.1個 refers to the number
of plastic fragments per fish (cf. リンゴを2個買った). 平均で means "on average".

> 大きさが5mm以下のプラスチックが平均で1.1個見つかりました。  
>  An average of 1.1 plastic fragments which were 5 mm or smaller in size were
> found.
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2017-03-12T18:58:43.927
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2017-03-12T18:58:43.927
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answer