**Core Concept**
The question tests the student's knowledge of intestinal parasitology, specifically the identification of ova and their correlation with the clinical presentation. The underlying concept is the ability to distinguish between different types of intestinal parasites based on their ova size and clinical manifestations.

**Why the Correct Answer is Right**
The ova size of 100 micrometres is characteristic of *Ascaris lumbricoides*, a common intestinal parasite that causes ascariasis. The clinical presentation of intermittent abdominal cramps and loose stools is consistent with ascariasis, which is often associated with intestinal obstruction or intestinal intussusception. The ova of *Ascaris lumbricoides* are large and yellowish in color, typically measuring 60-80 micrometres in length, but the size mentioned in the question could be due to the ova being laid in a degenerated state.

**Why Each Wrong Option is Incorrect**
* **Option A:** *Trichuris trichiura*, also known as whipworm, typically has ova measuring 50-60 micrometres in length, which is smaller than the size mentioned in the question. Therefore, it is unlikely to be the cause.
* **Option B:** *Ancylostoma duodenale*, a hookworm, has ova measuring 80-90 micrometres in length, but the size is not as large as 100 micrometres.
* **Option C:** *Strongyloides stercoralis*, a strongyloid worm, has ova measuring 80-90 micrometres in length, but the size is not as large as 100 micrometres.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the size of the ova can vary depending on the stage of development and the host's immune response. A thorough clinical evaluation, including stool examination and imaging studies, is necessary to confirm the diagnosis of intestinal parasitosis.

**Correct Answer:** A.