Intact buoyancy is a term used to describe（）.

A.the volume of all intact spaces above the waterline

B.an intact space below the surface of a flooded area

C.an intact space which can be flooded without causing a ship to sink

D.the space at which all the vertical upward forces of buoyancy are considered to be concentrated

The existing terrestrial radio system has a number of basic flaws which（）.

A.can be overcome by using traditional techniques

B.can not be overcome by satellite system

C.can be overcome by satellite and digital techniques

D.can not be tackled by any modern system