@amolpawar 

you will have to use script in script include and call it OR directly have script in advanced ref qualifier

something like this

Note: give correct choice value for A, B and the correct sysIds

javascript: var query='';
if(current.variables.firstVariable == 'choice value A')
query = 'sys_idINsysId1,sysId2'; // populate the 2 records which should be seen
else if(current.variables.firstVariable == 'choice value B')
query = 'sys_idINsysId3,sysId4'; // populate the 2 records which should be seen
query;

If you want to auto populate the reference variable based on option A or B selected then you can write onChange catalog client script on that drop down variable

something like this

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }

    if (newValue == 'choice A')
        g_form.setValue('variable2nd', 'sysId1');
    else if (newValue == 'choice B')
        g_form.setValue('variable2nd', 'sysId2');

}

If my response helped please mark it correct and close the thread so that it benefits future readers.