How to extract one variable from the whole Netcdf file

[Ming Yang <myang@xxxxxxxxxxxxx>]

Hi, guys
    I have a big nc file which contains tens of variables. What I want to do
now is to extract one of the variables from the whole nc file and generate
a new nc file containing  this varaible only. Do you know what is the
most efficient way to do this in Ferret? Or even other programs. Thank
you.

Ming