Classify the equations below as one of the following types of surfaces: A. parabolic cylinder,   B. ellipsoid,   C. elliptic paraboloid,
D. hyperbolic paraboloid,   E. elliptic cone,   and   F. hyperboloid.

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	1.	$4x^2+9y^2+z=0$
	2.	$36x^2+y^2+36z^2=36$
	3.	$y=z^2-x^2$
	4.	$x=y^2-z^2$

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