for the below questions use the following schema definition account$($accountid$,$ username, firstname, lastname$)$ digitalasset$($assetid$,$ description, dollarpricr$)$ transaction $($tranid$,$ accountid, timstamp$)$ transactiondetail$($tranid$,$ assetid, qty$,$ price$)$ what is the most appropriate index for digitalasset.description field?