From the options listed the strategy that would be least useful for helping students monitor comprehension of a text as they are reading is (A) breaking long sentences into short phrases
This option does not seem the most effective since it is a simplification or summary of sentences and the simplification does not always imply apprehension nor a correct hierarchization of the text.
A good paraphrase doesn’t simply substitute synonyms for the original words but substantially rewrites the passage—without changing its meaning or emphasis