**Core Concept**
The testicular volume at pre-pubertal age is an important indicator of normal testicular development. In boys, testicular volumes are typically measured using the Prader orchidometer, a tool consisting of 12 pairs of orchidometer testes of varying sizes.

**Why the Correct Answer is Right**
At pre-pubertal age, the normal testicular volume is less than 4 mL. This is because the testes are not yet undergoing the pubertal growth spurt, and the seminiferous tubules are not yet mature enough to support spermatogenesis. The testicular volume increases during puberty due to the growth of the seminiferous tubules and the Leydig cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because testicular volumes less than 1 mL are not typical for pre-pubertal boys, and may indicate a potential issue with testicular development.

**Option B:** This option is incorrect because testicular volumes greater than 4 mL are typically associated with pubertal development, which has not yet occurred in pre-pubertal boys.

**Option C:** This option is incorrect because testicular volumes of 1-4 mL are within the normal range for pre-pubertal boys, but there are multiple options that are more accurate.

**Option D:** This option is incorrect because testicular volumes greater than 4 mL are typically associated with pubertal development, which has not yet occurred in pre-pubertal boys.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the testicular volume can fluctuate due to various factors, such as temperature, hydration status, and stress. However, a consistent decrease in testicular volume may indicate a potential issue with testicular development or function.

**Correct Answer: C. 1-4 mL**