3. Given the equation $2 x^{2}-2 a x+3 a-4=0$ has no real roots, then the value of the algebraic expression $\sqrt{a^{2}-8 \rho \div 16}+12-a i$ is ( ).
(A) 2
(B) 5
(C) $2 a-6$
(D) $6-2 a$
3. $\mathrm{A}$ (Hint: From $\Delta<0$ we get $2<a<4$)