Answer
b)
Work Step by Step
Because the center of the ellipse is in the origin and the major axis is the x-axis, the equation of the ellipse here has the form $\frac{x^2}{b^2}+\frac{y^2}{a^2}=1$.
Here $a=2\\a^2=4$, $b=1\\b^2=1.$
Hence the equation is: $\frac{x^2}{1}+\frac{y^2}{4}=1$, thus the answer is b).
