The mother of a 9-month-old asks about adding new foods to his diet. The child is being breast-fed and takes formula and cereal when at the sitter’s. Which of the following would the nurse instruct the mother to do

A. Mix new foods with formula or breast milk.
B. Mix new foods with more familiar foods.
C. Offer new foods one at a time.
D. Offer new foods after giving formula or breast milk.

一天之中空气最新鲜的时间是（）。

A、上午10点左右，下午3至4点

B、中午12点

C、早晨7点前、晚上7点前后