Difficulty: Easy
Correct Answer: must be used to feed
Explanation:
Given data
Concept/Approach
When the focus is on technology as the thing acted upon, we require the passive voice: “must be used …”.
Option analysis
must be used to feed — correct passive infinitive after a modal. ✅must have been using, must be using — progressive aspects with an agented subject, which we do not have.must use having fed — ill-formed non-finite sequence.No correction required — original is ungrammatical.
Final Answer
must be used to feed the forces of change.
Discussion & Comments