Which of the Following Is the Equation of a Circle $x ^ { 2 } - y ^ { 2 } = 81$

Multiple Choice

Which of the following is the equation of a circle?

A) $x ^ { 2 } - y ^ { 2 } = 81$
B) $( x - 5 ) ^ { 2 } + y ^ { 2 } = 49$
C) $y = 9 x ^ { 2 } + 5$
D) $( x - 5 ) + ( y - 9 ) ^ { 2 } = 49$