Under 46 CFR §11.402(c)(1), an officer holding a tonnage-limited national endorsement as master may have all tonnage limitations removed by providing evidence of how much service on vessels of 1,600 GRT or more in the highest grade endorsed?

Why B is correct

46 CFR §11.402(c)(1) provides that when an applicant presents evidence of 6 months of service on vessels of 1,600 GRT or more in the highest grade endorsed, all tonnage limitations will be removed. The 12-month provision in §11.402(c)(3) applies specifically to able seamen holding a third mate endorsement.