**Core Concept**
Combination chemotherapy involves the use of multiple chemotherapeutic agents to target cancer cells through different mechanisms, increasing the effectiveness of treatment and reducing the risk of resistance. This approach is based on the principle of synergism, where the combined effect of multiple drugs is greater than the sum of their individual effects.

**Why the Correct Answer is Right**
The correct answer is **Low-grade lymphomas**, specifically indolent lymphomas. This is because combination chemotherapy is generally not indicated in low-grade lymphomas due to their indolent nature. These lymphomas grow slowly, and the use of combination chemotherapy can lead to significant toxicity without providing a significant survival benefit. In contrast, aggressive lymphomas, such as diffuse large B-cell lymphoma, are typically treated with combination chemotherapy.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Hodgkin's lymphoma** - Combination chemotherapy is actually the standard treatment for Hodgkin's lymphoma, and it has been shown to improve survival rates.
* **Option B:** **Small cell lung cancer** - Combination chemotherapy is a cornerstone of treatment for small cell lung cancer, and it is often used in combination with radiation therapy.
* **Option C:** **Ovarian cancer** - Combination chemotherapy is commonly used in the treatment of ovarian cancer, particularly in advanced stages.

**Clinical Pearl / High-Yield Fact**
When considering combination chemotherapy, it's essential to weigh the potential benefits against the risks of toxicity, particularly in patients with a history of comorbidities or organ dysfunction.

**Correct Answer: D. Low-grade lymphomas.**