Which reduction method eliminates diagonally opposite corners of a sample?

The quartering method is a sample reduction technique that effectively eliminates diagonally opposite corners of a sample to provide a more manageable and representative portion for testing. This process begins by dividing the sample into four equal quarters. By discarding two diagonally opposite quarters, it ensures that the remaining sample is still representative of the original while significantly reducing its size. Quartering is particularly useful in aggregate sampling as it helps to minimize bias by ensuring that the remaining material includes portions from different areas of the original sample, maintaining its overall characteristics.

The other options represent different sampling techniques that do not specifically involve the elimination of diagonally opposite corners, which is why they are not applicable in this context.