An analyst does research about revenue recognition. Which of the following criteria is not required for the recognition of revenue from the sale of goods under U. S. Generally Accepted Accounting Principles (U. S. GAAP) （）

A. There is evidence of an arrangement between buyer and seller.

B. The seller is reasonable sure of collecting money.

C. The amount of revenue can be measured reliably.

为了减小NDB的地损耗，最主要的措施是（）。

A.增加天线高度

B.铺设地网

C.加深接地线