Step 1: Understanding the Concept:
This question concerns the third case, plural form of the feminine gender of the pronoun 'idam' (this). In Sanskrit grammar, word forms change according to gender, number, and case.
Step 2: Detailed Explanation:
The feminine forms of the word 'idam' are as follows:
Nominative Case: इयम्, इमे, इमाः
Accusative Case: इमाम्, इमे, इमाः
Instrumental Case: अनया, आभ्याम्, आभिः
Dative Case: अस्यै, आभ्याम्, आभ्यः
Ablative Case: अस्याः, आभ्याम्, आभ्यः
Genitive Case: अस्याः, अनयोः, आसाम्
Locative Case: अस्याम्, अनयोः, आसु
From the table above, it is clear that the feminine form of 'idam' in the third case, plural is 'ābhíḥ'.
Step 3: Final Answer:
Therefore, the correct answer is 'ābhíḥ'.