The correct answer is A) A drill in its use shall be held once in every 3 months. The requirement for testing the line-throwing appliance is found in 46 CFR 199.180(d), which states that "A drill in the use of the line-throwing appliance must be conducted at least once every 3 months." This regular drill is necessary to ensure the crew's proficiency in operating the line-throwing device, which is an important safety equipment on board vessels. The other options are incorrect because B) requires quarterly drills and annual firing, which is more frequent than the 3-month requirement; C) requires firing the appliance every 3 months, which is not the same as a drill; and D) is incorrect as drills are required per the regulations.