Final answer:
Benedictine monks did indeed develop a form of sign language to adhere to their vows of silence, although it was not a comprehensive sign language as we understand it today.
Step-by-step explanation:
The statement that Benedictine monks invented a sign language to avoid breaking their vows of silence is true. Monastic communities, including the Benedictines, have a long history of using non-verbal communication to maintain silence, which is a key part of their spiritual discipline.
The use of manual signs among monks dates back to at least the 10th century. While not a fully developed sign language in the modern sense, these gestures were used extensively within the monastic setting to convey messages without verbal speech.