**Core Concept**
The question is testing the understanding of **fluid replacement therapy** in pediatric patients with severe diarrhea, focusing on the **World Health Organization (WHO) oral rehydration solution** and the calculation of fluid requirements based on the child's weight.

**Why the Correct Answer is Right**
For a child with severe diarrhea, the WHO recommends an oral rehydration solution to replace lost fluids and electrolytes. The calculation of fluid requirements is typically based on the child's weight, with the general guideline being 75 mL/kg over 4 hours for the first phase of treatment, followed by ongoing replacement based on stool output.

**Why Each Wrong Option is Incorrect**
**Option A:** Insufficient information is provided to assess its correctness.
**Option B:** Similarly, lacks necessary details to evaluate its accuracy.
**Option C:** Without specific details, this option cannot be properly assessed.
**Option D:** Also lacks the information needed for a thorough evaluation.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the treatment of severe diarrhea in children involves not just the initial fluid replacement but also ongoing assessment and adjustment of fluid therapy based on the child's clinical response and continued stool output.

**Correct Answer:** D. 100 ml/kg.