The correct answer is B. Their backpacks fully loaded
Explanation:
In language, an absolute phrase is one that contains a noun, a participle (word ended in -ing or -ed) and acts as an independent entity in a sentence usually modifying other words in it. Because of this, absolute phrase are usually placed at the beginning of sentences and are set apart by commas. This means, in the case of the sentence presented the one that is an absolute phrase is "Their backpacks fully loaded" because this is the section of the sentence with a noun "their backpacks" a participle "loaded" and that modifies the rest of the words which occurs in absolute phrases.
