Explanation:

- M1: This is the most liquid form of money supply. It includes cash in circulation and demand deposits at banks. It's essentially money that can be quickly used for transactions.

- M2: This measure includes all of M1, plus savings deposits, time deposits under a certain limit, and non-institutional money-market funds. These are slightly less liquid than M1, as they are not immediately available for transactions.

- M3: This consists of M2 plus large time deposits and institutional money-market funds. These components are even less liquid than those in M2.

- M4: This broad measure includes M3 along with some additional deposits. It incorporates the largest range of financial assets, making it the least liquid option.

Correct Answer: M4

.