Answer:
While the little boy and the pet dog raced ahead, the husband and wife found themselves comparing the possible effectiveness of each style against its appearance...
Explanation:
An adverbial phrase is a phrase or group of words that modifies the verb, adverb, and adjectives in a sentence. And if an adverbial phrase begins any sentence, then it should always be followed by a comma.
Among the given sentences, the second sentence contains an adverbial phrase that is set off with a comma. The adverbial phrase is "while the little boy and the pet dog raced ahead" which is then followed by a comma, separating it from the independent clause of the remaining sentence.
Thus, the correct answer is the second option/ sentence.
