Final answer:
The correct answer is option a. The 7-letter word that refers to relatives collectively is 'cousins', which fits the definition and has the correct number of letters.
Step-by-step explanation:
The student is asking for a 7-letter word that refers to relatives collectively. In the context of extended family, this term is inclusive of a variety of family members beyond the immediate nuclear family, which typically consists of parents and their children. When we think about the term that is 7 letters long and fits the definition of 'y'all's relatives, collectively,' the most appropriate answer from the given options is cousins.
Cousins refer to the children of one's aunt or uncle, or the children of one's parent's siblings. They are part of the extended family, which includes grandparents, aunts, uncles, and cousins.