  We prove in this paper the Ax-Lindemann-Weierstrass theorem for all mixed
Shimura varieties and discuss the lower bounds for Galois orbits of special
points of mixed Shimura varieties. In particular we reprove a result of
Silverberg in a different approach. Then combining these results we prove the
Andr\'e-Oort conjecture for any mixed Shimura variety whose pure part is a
subvariety of A_6^n.
