我国长途自动电话一般采用哪种计费方式？

已知一个扇形的半径为6cm，圆心角为150°，则这个扇形的面积为______cm²．

Dear sir,

Last year I buy a refrigerator in your store on Chang An Road. We all like shape of the refrigerator. And yesterday something went wrongly. It made a noise when turning on. At first it was low but gradually it became louder and louder. To make matter worse，it even stopped working. We all felt disappointing. I am writing to ask for help. Would you please find someone to repair them? I would be at home this weekend. Please call me before you come to here. My telephone number is 66065531. Thank you very much.

Li Ming

按双线互补的要求处理双线关系有两种方式，一是声画同一，二是（）

A.声画分离

B.声画协调

C.以声补画

D.声画对位

锅炉停止向外供汽时，要定时进行放水和上水，其目的是（）。

《国有土地使用证》、《集体土地所有证》和《集体土地使用证》均可以作为抵押权的法律凭证。