**Core Concept**
Developmental milestones are crucial indicators of a child's physical, cognitive, and emotional growth. At 6 months of age, infants typically exhibit specific abilities and skills that are essential for their overall development.

**Why the Correct Answer is Right**
At 6 months, infants usually sit up with support, roll over from their stomach to their back, and transfer toys from one hand to another. They also start to babble and coo, making sounds that resemble words. Moreover, they begin to show interest in their surroundings, tracking objects with their eyes and reaching for them.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because most infants at 6 months can sit up without support, not just with support. Sitting up straight with support is a milestone typically achieved at 5 months.

**Option B:** This option is incorrect because most infants at 6 months can transfer toys from one hand to another, demonstrating hand dominance and fine motor skills.

**Option C:** This option is incorrect because most infants at 6 months exhibit babbling and cooing sounds, not just crying.

**Option D:** This option is incorrect because most infants at 6 months show interest in their surroundings and track objects with their eyes.

**Clinical Pearl / High-Yield Fact**
At 6 months, infants typically triple their birth weight and develop sufficient head control to sit up without support. This is a critical period for development, and any significant delays or regressions should prompt a thorough evaluation.

**Correct Answer: A. Most infants at 6 months can sit up without support.**