The subject is 'uncle' because it is the one who make the action and response to the question: 'Who made the action exprimed throw the verb 'is eating' ? '
The subject of the sentence "My uncle is always eating peanut-butter sandwiches" is "uncle," as it indicates who is performing the action described by the verb. To find it, we look for who is doing the action in the sentence. The subject can be underlined as My uncle .
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