**Core Concept**
The question is testing the understanding of the management of vocal cord paralysis, particularly in the context of a condition that may be temporary, such as diphtheria. Vocal cord paralysis can result from various causes, including neurological disorders, trauma, or infections like diphtheria.

**Why the Correct Answer is Right**
In cases of vocal cord paralysis due to conditions like diphtheria, the paralysis is often temporary and may resolve spontaneously as the underlying condition improves. Diphtheria toxin can cause paralysis of the recurrent laryngeal nerve, leading to vocal cord weakness or paralysis. However, with appropriate treatment of the underlying infection, the paralysis may resolve on its own. In such cases, immediate surgical intervention is not necessary, and the patient should be managed conservatively.

**Why Each Wrong Option is Incorrect**
**Option A:** Gel foam injection of the right vocal cord is a type of medialization laryngoplasty, which is used to treat vocal cord paralysis by injecting a material into the vocal cord to improve its mobility. However, this procedure is typically reserved for cases of permanent vocal cord paralysis.

**Option B:** Fat injection of the right vocal cord is another type of medialization laryngoplasty, similar to gel foam injection. It is used to treat vocal cord paralysis by injecting fat into the vocal cord to improve its mobility. However, this procedure is also typically reserved for cases of permanent vocal cord paralysis.

**Option C:** Thyroplasty type-I is a surgical procedure used to treat vocal cord paralysis by implanting a material, such as Gore-Tex, into the vocal cord to improve its mobility. This procedure is typically reserved for cases of permanent vocal cord paralysis.

**Clinical Pearl / High-Yield Fact**
It is essential to differentiate between temporary and permanent vocal cord paralysis, as the management of the two conditions differs significantly. In cases of temporary paralysis, such as diphtheria, conservative management with observation and supportive care may be sufficient, while permanent paralysis may require surgical intervention.

**Correct Answer Line**
✓ Correct Answer: D. Wait for spontaneous recovery of vocal cord.