Answer:
Ed
Step-by-step explanation:
As per the performance ratings presented in the graphic chart, 'Ed' is the teacher who displays the most variable or fluctuating during these five years. His performance has remained shifting constantly from (1 to 4 between 2005-06, then from 4 to 2 between 2006-07, and again 2 to 4 in 2007-08 and 4 to 1 in 2008-09). On the contrary, the other teachers have been able to remain consistent for once at least.
- Jill remained consistent during 2005-07.
- Ralph's performance was steady during the year 2006-07 and 2008-09.
- Tina was stable during the period 2007-09.
- And Sam was able to perform consistently throughout the year 2008-09.
This observation validates the point that Ed has remained most inconsistent and exhibits the most variation during this span of five-years.