Medium of exchange can be defined as:（）

A. an asset that will allow people to transfer purchasing power form one period to the next.

B. an asset that can be easily and quickly converted to purchasing power without loss of value.

C. an asset that is used to buy and sell goods or services.

墩台基桩入土深度为12m，土质为软塑黏土，应采用（）。

A.锤击沉桩

B.静力压桩

C.射水沉桩

D.振动沉桩