Many of the soundings shown on the chart are derived from（）， Undue reliance should not be placed upon them.

Many of the soundings shown on the chart are derived from（）， Undue reliance should not be placed upon them.
A.complete and often very poor surveys
B.correct and often very good surveys
C.inadequate and often very old surveys
D.adequate and present surveys
正确答案：inadequate and often very old surveys