**Core Concept**
The question is testing the student's knowledge of the characteristic locations of cardiac vegetations in infective endocarditis. Cardiac vegetations are abnormal growths on the heart valves, typically caused by bacterial or fungal infections. They can be found on the atrial or ventricular surfaces of the valves, depending on the underlying pathology.

**Why the Correct Answer is Right**
Vegetations on the undersurface of atrioventricular (A.V.) valves, such as the mitral or tricuspid valves, are characteristic of subacute bacterial endocarditis (SBE). This is because the undersurface of these valves is more prone to turbulent blood flow, which creates a conducive environment for bacterial colonization and vegetation formation. The presence of vegetations on the undersurface of A.V. valves is a hallmark of SBE, often associated with Streptococcus viridans or Staphylococcus aureus infections.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because vegetations on the undersurface of A.V. valves are not typically associated with acute rheumatic fever, which usually involves the mitral valve but tends to cause inflammation and scarring rather than vegetation formation.

**Option B:** This option is incorrect because vegetations on the undersurface of A.V. valves are not characteristic of non-bacterial thrombotic endocarditis (NBTE), which typically involves the ventricular surface of the valves and is associated with hypercoagulable states or malignancy.

**Option C:** This option is incorrect because vegetations on the undersurface of A.V. valves are not typically associated with infective endocarditis caused by enterococci, which more commonly involves the atrial surface of the valves.

**Clinical Pearl / High-Yield Fact**
To remember the characteristic locations of cardiac vegetations, recall the "TEA-ETEA" mnemonic: "Turbulent" (undersurface of A.V. valves in SBE), "Embolic" (atrial surface in SBE), "Acute" (ventricular surface in NBTE), "Enterococcal" (atrial surface, often in older patients).

**Correct Answer:** C.