**Core Concept**
Cranberry juice has been traditionally used to prevent and treat urinary tract infections (UTIs), with the primary mechanism of action being the prevention of bacterial adhesion to the bladder and urinary tract walls. The exact mechanism is attributed to the presence of proanthocyanidins, which inhibit the expression of adhesins on the surface of uropathogenic bacteria.

**Why the Correct Answer is Right**
The proanthocyanidins in cranberry juice prevent the adhesion of bacteria to the bladder and urinary tract walls by inhibiting the expression of adhesins on the surface of uropathogenic bacteria. This prevents the bacteria from colonizing and causing infection. The regular consumption of cranberry juice has been shown to reduce the incidence of UTIs in women by preventing bacterial adhesion.

**Why Each Wrong Option is Incorrect**
* **Option A:** Orange juice does not have any proven benefits in preventing UTIs. Its high sugar content may even contribute to the development of UTIs due to the presence of sugars in the urine.
* **Option B:** Grapefruit juice has not been studied extensively for its effects on UTIs, and its high acidity may even irritate the bladder and urinary tract, increasing the risk of UTIs.
* **Option D:** Pineapple juice has anti-inflammatory properties, but it does not have any proven benefits in preventing UTIs.

**Clinical Pearl / High-Yield Fact**
Cranberry juice should be consumed regularly to prevent UTIs, and it may be particularly beneficial for women who experience recurrent UTIs.

**Correct Answer:** C. Cranberry juice.