A tangent to the hyperbola x²/4−y²/1=1 meets ellipse x²+4y²=4 in two distinct points .
Then the locus of midpoint of this chord is
A. (x²+4y²)2=4(x²−4y²)
B. (x²−4y²)2=4(x²+4y²)
C. (x²−4y²)2=4(x²+y²)
D. none of these