## Core Concept
The child's symptoms of bed-wetting at night, but not during the day, along with a urine specific gravity of 1.020 and normal other tests, suggest **nocturnal enuresis**, also known as nighttime bedwetting. This condition can be related to issues with **antidiuretic hormone (ADH) secretion** or **renal concentrating ability**.

## Why the Correct Answer is Right
The child's **urine specific gravity of 1.020** indicates that the kidneys are capable of concentrating urine. A normal to high specific gravity suggests that the issue may not lie with the kidneys' ability to concentrate urine but potentially with **ADH secretion patterns**. Nocturnal enuresis can often be managed with behavioral modifications and, in some cases, medication that affects ADH levels or its action.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically involves limiting fluid intake before bedtime and using the bathroom right before sleep. While useful, this option does not directly address potential underlying issues like ADH secretion.
- **Option B:** This involves waking the child up at intervals during the night to use the bathroom. This could be effective but might not be practical or directly address the underlying cause.
- **Option C:** This option involves **desmopressin**, a synthetic analogue of ADH. Given the child's ability to concentrate urine (suggesting normal renal function), **desmopressin** could be particularly effective if the issue is related to nocturnal ADH deficiency.
- **Option D:** This option might involve more invasive or unnecessary diagnostic tests given that the child's other tests are normal.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **desmopressin** is often the first-line treatment for **nocturnal enuresis** (bedwetting) in children, especially when there's a suspected issue with nocturnal ADH secretion. It's crucial to rule out underlying anatomical or neurological issues but in cases with normal tests, **desmopressin** can be very effective.

**Correct Answer: C. desmopressin.**