According to 14 CFR Part 107, the remote pilot in command (PIC) of a small unmanned aircraft planning to operate within Class C airspace
Amust use a visual observer.
Bis required to file a flight plan.
Cis required to receive ATC authorization.✓ Correct answer
Why →Class C airspace requires prior ATC authorization per § 107.41. Visual observers are never required by Part 107 (though recommended), and flight plans are a manned aviation concept. Remote pilots do not file flight plans. Authorization is the mandatory requirement.
Field note →Class B, C, and D all require prior authorization. Class G requires nothing. Class E surface requires authorization. Class E non-surface (above 700 ft AGL) is accessible without authorization for typical low-altitude sUAS ops.