if C1_eco is the first question, the choice filter on question_2 should say
selected-at(${C1_eco}, filter)
Where filter is the name of the filter column you have added to your choices list. It can be a copy of the list.
e.g. here the filters are 'country' and 'region'. you could try the same but your filter would be 'city' and it'd be a direct copy of the list, a one to one match.
so add a column called 'eco_filter', copy the names from the list into it, then have your choice filter on the second question be selected-at(${C1_eco}, eco_filter)