"The average price of a gallon of milk is $3.50, according to the New York Times" is a complete source citation in a speech.
a) "The average price of a gallon of milk is $3.50, as per a credible source."
b) "According to a recent study, the average price of a gallon of milk is $3.50."
c) "As stated by the New York Times, the average price of a gallon of milk is $3.50."
d) "The average price of a gallon of milk is $3.50, as reported by a reliable source."