Final answer:
The correct answer to fill in the blanks describing the group's journey is A) Rapids, destination, as these terms correlate with the context of a river journey and reaching the journey's end.
Step-by-step explanation:
The sentence completion question asks for the correct terms to fill in the blanks describing the journey the group is undertaking. From the information provided, we know that the group encounters challenges traveling along a river and that these challenges are related to waterfalls and the ultimate goal or destination of their journey.
The answer is A) Rapids, destination, as this option provides words that fit the context of a river journey. 'Rapids' suggests a challenging, fast-moving section of a river often found approaching waterfalls, which matches the description given in the provided references. 'Destination' is the term used to describe the place at the end of a journey, which is a fitting conclusion for the group's adventure.