单项选择题
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
单项选择题 On this chart only the principle （） to navigation are shown．
单项选择题 To agree with larger scale chart，latitudes taken from this chart should be increased （） about 8 seconds．
