Liquidity is the ability to convert the asset into cash quickly.
If an asset takes more time to get converted into cash, then the asset is less liquid.
From this explanation we can say Currency is the most liquid form of asset.
When Compared with saving deposits, Current deposits has less restriction with respect to banking transaction. So current deposits are more liquid than savings deposits.
Since Demand Deposits include both Current and Saving Deposits in terms of liquidity - Demand deposits are more liquid than saving deposits.
Time Deposits would be least liquid among the given options.
Hence option D is correct