Filter Data Issue

Hi All , 

I am facing one issue Appian

I have Two Filter Area and Zone  to extract the data in table  example like 

Area is multiple drop down having value's A , B ,C , D , E , F , G 

and 

Zone  is multiple drop  down having a , b , c, d , e , f , g ,h  , i 

if we select the Area A then Zone should show  b , c , d instead of a , b , c , d , e , f ,g , h , i  similarly if we select Area B Zone should show e , f , g instead of a , b , c ,d ,e , f ,g , h ,i   so what would be condition 

i m using like this 

a!multipleDropdownField(
label: "Area",
labelPosition: "ADJACENT",
choiceLabels: index(
local!varriable(Exp Rule ).data,
"field 1",
null
),
choiceValues: index(
local!varriable.data,
"field1",
null
),
value: local!selectedArea,

saveInto: {local!selectedArea,a!save(local!pagingInfo1,local!fPagingInfo2)},
validations: {}
),

a!multipleDropdownField(
label: "Zone",
labelPosition: "ADJACENT",
choiceLabels: index(
local!varriable2(Exp Rule ).data,
"field2 ",
null
),
choiceValues: index(
local!varriable2.data,
"field2",
null
),
value: local!selectedZone,

saveInto: {local!selectedZone,a!save(local!pagingInfo1,local!fPagingInfo2)},
validations: {}
),