Final answer:
Infants first recognize differences in speech sounds during the sensorimotor stage, which is from birth to about 2 years old but have a prelinguistic ability even before birth to distinguish the sounds of their mother's language from others.
Step-by-step explanation:
Infants are first able to recognize differences in speech sounds during the sensorimotor stage, which is the first stage in Piaget's theory of cognitive development. During this period, from birth through age 2, a child learns about the world through their senses and motor behavior. Research has shown that newborns demonstrate a preference for their mother's voice and can discriminate between the language spoken by their mother and other languages. This early ability to discern between different phonetic sounds is evident as infants show preferences even for faces that are moving in synchrony with the audio of spoken language.
The ability to recognize differences in speech sounds evolves very early in life, starting before birth, and continues to develop as babies are exposed to spoken language around them. By the time they are about 1 year old, they can only discriminate among those phonemes that are used in the language or languages of their environment. Therefore, the correct answer to the question is 'd) Prelinguistic stage' assuming that the student is referring to a period before the language acquisition begins, typically considered to be before the sensorimotor stage.