In January there was a large drop in the number of new houses sold, because interest rates for mortgages were falling and many consumers were waiting to see how low the rates would go. This large sales drop was accompanied by a sharp rise in the average price of new houses sold.
Which of the following, if true, best explains the sharp rise in the average price of new houses ？（）

A．Sales of higher-priced houses were unaffected by the sales drop because their purchasers have fewer constraints limiting the total amount they pay.

B．Labor agreements of builders with construction unions are not due to expire until the next January.

C．The prices of new houses have been rising slowly over the past three years because there is an increasing shortage of housing.

D．There was a greater amount of moderate-priced housing available for resale by owners during January than in the preceding three months.

E．Interest rates for home mortgages are expected to rise sharply later in the year if predictions of increased business activity in general prove to be accurate.

前牙反矫治时，拔牙不取决于以下哪项因素（）

A.上牙弓的拥挤程度

B.上牙弓的生长潜力

C.牙弓突度

D.下颌牙弓的拥挤程度

E.年龄