What diameter range is acceptable for the tamping rod specified in this testing method?

The correct choice, which indicates that the acceptable diameter range for the tamping rod is 16 mm ± 2 mm, is based on established specifications for testing procedures involving concrete and cement mixtures. The requirement for the tamping rod's diameter is specified to ensure consistency in the compaction of concrete samples during testing.

Using a rod that is precisely 16 mm allows for a standard method of tamping that ensures uniformity in the compaction process, as the rod's size contributes directly to the quality of the sample being tested. The specified tolerance of ± 2 mm provides manufacturers and users with a small range of acceptable sizes (between 14 mm to 18 mm), ensuring that the rod can still perform its function effectively while accommodating slight variations that might occur during production or handling.

In contrast, the other options do not adhere to the established guidelines which define the tamping rod's diameter specifications. This makes option B the best choice as it reflects the necessity for having a diameter that meets precise testing requirements.