Which verbal milestone is expected for a 4-month-old infant?

For a 4-month-old infant, the expected verbal milestone is to coo and gurgle. At this age, infants are developing their vocalization skills and typically begin to produce cooing sounds which consist of prolonged vowel sounds, along with gurgling noises. This is an important stage in language development as it indicates the infant's ability to experiment with sounds and engage in early communication.

As for the other choices, they reflect developmental milestones that are generally not expected until later in infancy or toddlerhood. Speaking in full sentences is a milestone that typically emerges much later, usually around the age of 2 years. Babbles with different tones appear closer to 6 months of age when infants start to combine consonants and vowels in a more complex manner. Responding to their name is usually observed around 6 to 9 months when infants start to recognize familiar words, including their own name. At 4 months, while infants may start to show recognition of sounds, it is not developed enough for them to consistently respond to their name.