**Core Concept**
The underlying principle being tested is the process of hemagglutination and its reversal, which is a crucial aspect of virology, particularly in the context of the influenza virus. Hemagglutination is the aggregation of red blood cells caused by certain viruses, including influenza.

**Why the Correct Answer is Right**
The reversal of hemagglutination is attributed to the action of the enzyme neuraminidase, which is present on the surface of the influenza virus. This enzyme breaks down the sialic acid receptors on the surface of red blood cells, preventing the hemagglutinin from binding and thus reversing the agglutination.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not accurately describe the reversal of hemagglutination.
**Option B:** Similarly, this option is incorrect as it does not relate to the reversal process.
**Option C:** This choice is also incorrect as it is not associated with the phenomenon in question.

**Clinical Pearl / High-Yield Fact**
The reversal of hemagglutination is an important concept in virology, particularly for understanding the lifecycle of the influenza virus and developing diagnostic tests.

**Correct Answer:** D. Hemagglutination inhibition.