Answer
Find out the area of an ellipse .
To proof
Formula

where a and b are major and minor axis of the ellipse
As given
In an ellipse
the major axis 20 m and the minor axis 10 m

put all the value in the formula
we get
Area of an ellipse = 3.14× 10× 20
= 628 m²
option (B) is correct
Hence proved