On board small passenger vessels, fill lines and sounding pipes of gasoline tanks must extend directly __________.

Correct Answer: Option B — to within one-half of their diameter from the bottom of the tank

46 CFR 182.440 requires fill lines and sounding pipes for gasoline tanks to extend to within one-half of their diameter from the bottom of the tank. This design minimizes static electricity buildup and prevents the splashing of fuel, which could create hazardous vapor concentrations during refueling or sounding operations.