Surveying
For a line AB

the forebearing of AB and back bearing of AB differ by 180°
the forebearing of AB and back bearing of BA differ by 180°
none is correct
both (A) and (B) are correct

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Surveying
The difference between a level line and a horizontal line is that

level line is normal to plumb line while horizontal line may not be normal to plumb line at the tangent point to level line
horizontal line is normal to plumb line while level line may not be normal to the plumb line
both are same
level line is a curved line while hori-zontal line is a straight line

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