Add the phrase that completes a thought in
the sentence.

challenging problems

Explanation:

Whatever completes the text would have be something that relates to the problems that are to be solved as this is the subject of the sentence and it would have to be in the negatives due to the use of the word "unfortunately".

The best option is therefore the above because too many challenging problems relates to the subject of problems and is not a good thing.

- "he is a very real person and his intent isn't to influence us vonnegut addresses this towards the end of the letter when he says, if we choose to curse, that is by our own individual means."

b. our party quickly made its way into the cave / but we failed to find our host [the cyclops] himself inside.