Which of the following sentences is correctly punctuated?

The correct answer is the sentence that uses "Let's," which is a contraction for "let us." In this context, the sentence "Let's eat Grandma." includes the necessary apostrophe to indicate the contraction, clearly showing that the speaker is inviting Grandma to eat with them, not suggesting that they are going to eat Grandma herself.

The punctuation in this choice effectively clarifies the intended meaning, which is essential in preventing any confusion or ambiguity. The use of the comma after "eat" also provides proper separation between the invitation and the person being addressed, enhancing clarity further.

Other options fail to convey the correct meaning due to grammatical errors. The version that simply states "Lets" without an apostrophe misleads the reader into thinking "lets" is a verb form meaning "to allow," which changes the meaning completely. The option that attempts to use "Lets'" incorrectly places an apostrophe at the end, which does not form a proper contraction and is not grammatically valid.