充氮机使用前检查（）合格，检查充气管道及接头完好，连接可靠。

A.压力表

B.电源线

C.油箱

D.管道

A merchant paid $300 for a shipment of x identical calculators. The merchant used 2 of the calculators as demonstrators and sold each of the others for $5 more than the average (arithmetic mean) cost of the X calculators. If the total revenue from the sale of the calculators was $120 more than the cost of the shipment, how many calculators were in the shipment ？（）

A.24

B.25

C.26

D.28

E.30