limn→∞1+2+3++nn2=limn→∞n(n+1)2n2=12，
故选C．
债券信用评级机构应及时跟踪发行人的债券资信变化情况，债券资信发生重大变化的，应及时调整债券信用评级，并及时向市场公布。（）
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.
