A mother and her young son got into a bus in New York City and sat down. The bus conductor（售票员） came to them for their money. The mother said, "I want one ticket（票） to Central Park, "and gave him two dollars. The conductor looked at the small boy for a few seconds and then asked him, "How old are you, young man?"  The mother just began to speak, but the conductor stopped her, and the boy said, "I'm four years old at home, and two and a half on buses and trains."  The mother felt shamed（羞愧）， so she took another dollar out of her bag and gave the money to the conductor. The conductor gave her one and a half tickets.

下列词语中加线字的字音，全都正确的一组是(　　)