Answer
The numbers on the $x$-axis must be in ascending order.
Work Step by Step
The time plot does not show increasing numbers on the $x$-axis: after 99 comes 00. Even though 00 wants to represent a short form for 2000, we cannot have a sequence of numbers other than an increasing one.
We can either write all years using 4 digits, or use 0 for 1996, 1 for 1997 and so on.
