select options in function module

hi friends, pls help me reg my query.

I have wERKS select-options

on the selection screen.

(This same thing, i want to pass in FM)

2. So in FM, I have used the

TABLES parameter (Not import, nor export)

3. And the type given is

WERKS_RANG

i defined it like

plant type WERKS_RANG

(This WERKS_RANG has 4 fields,

just like a select option

SIGN

OPTION

LOW

HIGH

)

4. Then inside fm,

i used SELECT Query,

and use IN WERKS.

below is my code in FM.

select lgort labst

from mard

into table imard1

where PLANT in werks

and material1 = matnr.

but i am getting an error "field plant is unknown". i have defined it under tables parameter..pls help

how shud i get the values i enter in select option for main program in se38 to function module field 'plant'...