Cats are killers, and they are threatening the songbird population. many people blame the strays that must hunt to survive. however, even well-fed pets that are allowed outside hunt, because it is their instinct. what is the  best  way to end this paragraph? therefore, they should be kept inside. for example, they should be kept inside. however, they should be kept inside. to summarize, they should be kept inside. 

Therefore, they should be kept inside.

Explanation:

For example, they should be kept inside IS WRONG because it is the end of the paragraph so you wouldn't say for example because that is an elaboration starter.

However, they should be kept inside.  IS ALSO WRONG because earlier in the paragraph they used however and it would not make sense to use it again.

To summarize, they should be kept inside. IS ALSO WRONG because it is a paragraph not an essay so it to summarize wouldn't make sense.

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