Observe the graph:
It is an ellipse.
Cosider option (a) equation is .
Compare with .
.
Since, the equation represents an ellipse.
Option (a) is correct.
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=749a679fbb509e502f96d04bdf7df377.png\")
..![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=4e0c35a3395f9e0fc7855b2b2ff789ee.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=7e8f960420d3cd4c758723056fc02c85.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=48a3f721f83c76f3d99bf3a583293245.png\")
![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=eab01704892b64c1dbf9114733073add.png\")
the equation represents an ellipse.