4. A 24-hour digital clock shows the time in hours and minutes.
How many times in one day will it display all four digits $2,0,1$ and 9 in some order?

A 6
B 10
C 12
D 18
E 24
4. B In order from $00: 00$, the times when the digits $2,0,1,9$ appear in some order are $01: 29,02: 19$, $09: 12,09: 21,10: 29,12: 09,19: 02,19: 20,20: 19$ and $21: 09$. So, in total, there are ten such times.