**Core Concept**
The question is testing the patient's stool examination findings and identifying the cause of diarrhea. The key concept here is the size of the ova, which is less than 100 μm.

**Why the Correct Answer is Right**
The size of the ova is a crucial factor in diagnosing parasitic infections. Ova less than 100 μm in size are typically associated with **Toxocara** species, which are roundworms that can cause toxocariasis. The most likely cause of diarrhea in this case is a parasitic infection, and the size of the ova points towards Toxocara. Toxocara ova are ingested through contaminated food or water, and the larvae can cause intestinal infection leading to diarrhea.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not provide any information about the size of the ova. Without knowing the size, it is difficult to determine the cause of diarrhea.
* **Option B:** This option is incorrect because it refers to a different type of parasite, Giardia, which can cause diarrhea but is not associated with ova less than 100 μm in size.
* **Option C:** This option is incorrect because it refers to a different type of parasite, Ascaris, which can cause diarrhea but is associated with ova larger than 100 μm in size.

**Clinical Pearl / High-Yield Fact**
Remember that the size of the ova is a critical factor in diagnosing parasitic infections. Always consider the size of the ova when interpreting stool examination findings.

**Correct Answer:** A. This option is correct because it does not provide any information about the size of the ova, making it an incomplete answer.