Final answer:
The little digastric muscle opposes the entire group of muscles of mastication, by playing a role in depressing the mandible as opposed to the action of elevation performed by the muscles of mastication.
Step-by-step explanation:
The correct answer to the question 'In one of its actions, the little ____________ muscle opposes the entire group of ____________' is A) digastric; muscles of mastication. The digastric muscle is part of the suprahyoid muscles which help in elevating the hyoid bone and the larynx during swallowing; it also plays a role in depressing the mandible, which is in contrast to the action of the muscles of mastication (including the masseter and temporalis), which primarily elevate the mandible for closing the jaw during chewing.