The correct answer is D. No error.
The sentence is grammatically correct. It is a complex sentence with two independent clauses joined by a comma and a coordinating conjunction (and). The first independent clause is “While walking slowly in the park.” The second independent clause is “a mad dog suddenly attacked him from behind.”
The sentence is also well-written. It is clear and concise, and it flows smoothly. The word choice is appropriate, and the sentence is free of errors in grammar, punctuation, and spelling.
Here is a breakdown of each option:
- Option A: While walking slowly in the park. This is the beginning of the first independent clause. It is grammatically correct.
- Option B: on a quiet summer afternoon. This is an adverbial phrase that modifies the verb “walking.” It is grammatically correct.
- Option C: a mad dog suddenly attacked him from behind. This is the beginning of the second independent clause. It is grammatically correct.
- Option D: No error. This is the correct answer. The sentence is grammatically correct.