**Core Concept**
At 10 months of age, infants typically exhibit certain developmental milestones, such as sitting without support, crawling, and standing while holding onto furniture. These skills are essential for normal motor development.

**Why the Correct Answer is Right**
The correct answer is related to the child's inability to perform a specific action that is expected at this age. Typically, by 10 months, infants should be able to sit without support and may start to cruise along furniture while holding on. The inability to sit without support suggests a delay in gross motor development, which may be due to muscle weakness, neurological issues, or other underlying conditions. This skill is a critical milestone, and its absence may indicate the need for further evaluation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.
**Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
It is essential to assess infants' developmental milestones regularly, as delays can indicate underlying issues. The American Academy of Pediatrics recommends using standardized tools, such as the Denver Developmental Screening Test, to screen for developmental delays.

**Correct Answer:** D. Sitting without support.