The guide words on a dictionary page are typically the first and last words on that page, which help the user locate words quickly. In your list, the guide words would likely be the ones that are in alphabetical order, which means they would represent the first and last entries on that hypothetical page.
In this case, the correct pair of guide words is:
acumen and adactyly
"Acumen" would be the first word on a page, and "adactyly" would be a word that comes later, making them a suitable pair of guide words.