Let G be a filtered Lie conformal algebra whose associated graded conformal
algebra is isomorphic to that of general conformal algebra gc1. In this
paper, we prove that G≅gc1 or grgc1 (the associated graded
conformal algebra of gc1), by making use of some results on the second
cohomology groups of the conformal algebra \fg with coefficients in its
module Mb,0 of rank 1, where \fg=\Vir\ltimes M_{a,0} is the semi-direct
sum of the Virasoro conformal algebra \Vir with its module Ma,0.
Furthermore, we prove that grgc1 does not have a nontrivial
representation on a finite \C[\partial]-module, this provides an example of a
finitely freely generated simple Lie conformal algebra of linear growth that
cannot be embedded into the general conformal algebra gcN for any N