Which space cannot be deducted from gross tonnage when calculating net tonnage?

Correct Answer: Option B — Forepeak ballast tank

Deductions from gross tonnage to determine net tonnage are governed by 46 CFR 69.61. Spaces like the forepeak ballast tank are not deductible because they are considered part of the vessel's structure or ballast system, rather than spaces used for the carriage of cargo or the accommodation of the crew.