The correct answer is C. A high capacity brake is required to hold a load approaching the breaking strength of the mooring line, but it is required to slip at a lower tension to avoid mooring line breakage. This is because if the brake could hold the full breaking strength of the mooring line, the line itself could break, which would be unsafe. The brake is designed to slip at a lower tension to prevent the line from breaking under excessive loads. The other options are incorrect because A and B do not allow for any slippage of the brake, which is necessary to avoid line breakage, while D requires a low capacity brake, which would not be able to hold loads approaching the line's breaking strength.