A standard for submission of electronic contest logs✓Correct answer
A method of exchanging information during a contest QSO
The most common set of contest rules
A digital protocol specifically designed for rapid contest exchanges
Explanation
Cabrillo is the plain text file layout that contest sponsors require when a log is submitted electronically: a header describing the entry followed by one line per contact. It is not a set of contest rules, an on-air exchange, or an over-the-air protocol.