The mother of a 2-year-old child tells the nurse that her baby is using a potty seat but is still having problems toilet-training. Which of the following suggestions by the nurse would he most appropriate（）

A. Offer the child more praise each time.

B. Use a potty chair instead of a potty seat.

C. Focus on the "accidents" that occur during training.

D. Defer training until the child is developmentally ready.

“信息经济”是由（）提出的。