Question

what type of context clue is used to determine the meaning of
after many decades of human manipulation, english bulldogs are so far from their natural ancestors that they commonly suffer from abnormalities, such as small airways and closed nostrils. our efforts to breed so many of these dogs have diluted the bloodline, thinning and weakening it further with every generation. rather than creating a sustainable breed of dog, we have created an unsupportable dog breed that cannot be maintained for much longer.
use context clues to define sustainable.

Explanation:

To determine the context clue for "thinning" (or the relevant word), we analyze the text. The sentence "Our efforts to breed so many of these dogs have diluted the bloodline, thinning and weakening it further" shows that "thinning" is related to reducing or making less (like diluting/weakening). The options: "thinned out" matches the idea of reducing in number/quantity (as thinning the bloodline would thin out the breed's genetic pool), "cleaned" doesn't fit, "destroyed or eliminated" is too extreme. So the context clue type here is probably "example" or "explanation" (but for the meaning of "thinning", the correct match is "thinned out" as the context shows the bloodline is being reduced, so the context clue is a synonym or explanation via the surrounding text about diluting/weakening. Wait, the question is "What type of context clue..." but the options given (thinned out, cleaned, destroyed or eliminated) seem to be for the meaning of a word (maybe "thinning"?). Wait, the text: "thinning and weakening it further" – so "thinning" here is about reducing the bloodline's quality/quantity. "Thinned out" is a synonym - so the context clue type would be "synonym" (since "thinned out" is a synonym for the meaning of "thinning" in the context). But the options are the meanings, not the clue types. Wait, maybe the question is to find the correct meaning of a word (like "thinning") using context. Let's re-express: The text says "diluted the bloodline, thinning and weakening it further". So "thinning" here means reducing the number or quality, so "thinned out" (reducing in number/quantity) is correct. "Cleaned" is irrelevant, "destroyed or eliminated" is too strong (it's just thinned, not destroyed). So the correct option is "thinned out" as the meaning, using the context of diluting and weakening the bloodline (so the context clue is "synonym" or "explanation" via the related words diluting/weakening, and the correct meaning is thinned out.

Answer:

thinned out