Final answer:
The corrected sentence is: "Mr. Smithers's dog, which is almost as tall as a horse, always knocks me over when we play."
Step-by-step explanation:
The revised sentence includes necessary punctuation to improve clarity and structure. The comma after "dog" sets off the nonrestrictive clause "which is almost as tall as a horse." This comma is crucial as it provides additional information about the dog but is not essential to understanding which dog is being referred to. Additionally, the use of an apostrophe after "Smithers" and the following "s" ('Smithers's') signifies possession, indicating that the dog belongs to Mr. Smithers. This punctuation helps to create a grammatically correct sentence that conveys the intended meaning more clearly.
Furthermore, the insertion of commas before and after the clause "which is almost as tall as a horse" helps set it apart from the main clause. This use of punctuation aids in avoiding ambiguity by separating the descriptive clause from the main sentence. It offers a better flow to the sentence while providing additional information about the dog's size in relation to a horse. Overall, the inclusion of these punctuations enhances readability and comprehension for the reader, ensuring the sentence is grammatically correct and effectively conveys the intended message.