Let $A, B, C, D$ and $E$ be five points marked in clockwise order, on the unit circle in the plane (with centre at origin). Let $\alpha$ and $\beta$ be real numbers and set $f(p)=\alpha x+\beta y$ where $P$ is a point whose coordinates are $(x,y)$. Assume that $f(A)=10, f(B)=5, f(C)=4$ and $f(D)=10$. Which of the following are impossible?
a) $f(E)=2$
b) $f(E)=4$
c) $f(E)=5$