Since in the certification questions you have to choose the "best" option, I think the answer that is more accurate is C) Sequence Activities.
Even though all the responses are outputs of the time management knowledge area, the option "Sequence Activities" could be less invasive, since it consists of establishing the relations and order between the activities in the project schedule network diagram.
For the other part, defining activities, estimating activity resources, and estimating durations involve major changes in the respective project documents. Saving Changes...
Love can sweep you off your feet and carry you along in a way you've never known before. But the ride always ends, and you end up feeling lonely and bitter. Wait. It's not love I'm describing. I'm thinking of a monorail.