**Core Concept**
The "cruising" milestone is a significant development in infants, indicating gross motor skills development. It is characterized by the ability to move along furniture or other stable objects while holding on for support, demonstrating a major step towards independent ambulation.

**Why the Correct Answer is Right**
Cruising is a precursor to walking and is typically achieved around 10 months of age. At this stage, infants have developed sufficient strength and balance to move their legs and maintain their center of gravity while holding onto a stable object for support. This milestone is a reflection of the maturation of the neuromuscular system, particularly the development of the hip and leg muscles. The ability to cruise also indicates improved balance and coordination.

**Why Each Wrong Option is Incorrect**
**Option A:** 8 months is too early for most infants to achieve the cruising milestone, as they typically need a few more weeks to develop the necessary strength and balance.
**Option C:** 13 months is too late, as most infants have already started walking independently by this age.
**Option D:** 15 months is significantly beyond the typical age range for cruising, as most infants have mastered walking by this age.

**Clinical Pearl / High-Yield Fact**
Remember that every infant develops at their own pace, and the timing of milestones can vary. However, if an infant is not cruising by 12 months, it may be a cause for concern and warrants a pediatrician's evaluation.

✓ Correct Answer: B. 10 months