The height of a light is measured from which reference plane?（）

Attention is called to the fact that in many cases pipelines are not （） and charted depths may be decreased by up to 2 meters．

Clearances of bridges and overhead cables below Bonneville Dam refer to heights in feet above mean （）.

As these features are not all charted，special caution should be exercised （） vessels navigating in the vicinity.

Attention is called to the fact that in many cases charted depths may be decreased by up to （）.

Due to lapse of time the risk in these areas to surface navigation is now considered （）than the ordinary risks of navigation，but a very real risk still exists with regard to anchoring，fishing or any form of submarine or seabed activity.

The Earth has the shape of a(n) （）.

The period at high or low tide during which there is no change in the height of the water is called the （）.

The distance between any two meridians measured along a parallel of latitude and expressed in miles is the （）.

In Admiralty Sailing Directions，bands is the word used to indicate（）marking．