Problem in Displaying default values in Dropdown in webdynpro

Hi Experts,

    Here Iam displaying one internal table values in a wd table.When Iam displaying

the table 1st,2nd columns are displayed successfully here the problem is with 3rd column

which is a dropdown by key.Below is sample screen.

      In the above, 3rd column having lt_tab(yes,no,na) but there is no default values appering either yes

or no or na.If the default value is yes then user may modified this yes and replace this yes with no or na

(which is alredy there in the itab of dropdown by key).Anyone could you give the suitable solution for this

is grately appreciated....

                      By default we need to display one value from the listed  values of dropdownby key,user

can modified this by selecting any one of the remaining values of dropdown..

Regards,

kranthi