Which of the following indicates a significant problem in an infant's communication system?

• A. The infant does not babble or make any vocal sounds by 12 months of age.
• B. The infant responds to loud noises by startling.
• C. The infant smiles in response to familiar faces.
• D. The infant occasionally cries when hungry or tired.

Answer: (A)

Verified step by step guidance

1. Understand that infant communication development follows typical milestones, such as making vocal sounds (babbling) by around 6 to 9 months and responding to stimuli like loud noises or familiar faces.
2. Identify that a significant problem in an infant's communication system would be a delay or absence of expected vocal behaviors, such as not babbling or making any vocal sounds by 12 months, which is beyond the typical developmental window.
3. Recognize that responses to loud noises (startling) and social smiles to familiar faces are normal developmental behaviors and indicate sensory and social engagement, not communication problems.
4. Note that occasional crying when hungry or tired is a typical form of infant communication and does not indicate a problem.
5. Conclude that the absence of babbling or vocal sounds by 12 months is a red flag for communication delays and warrants further evaluation.