According to a recent study, the decrease in percentage of citizens with obesity so that is was the lowest in a decade suggests that public awareness campaigns and good health initiatives may be paying off.
Choices
A - so that is was the lowest in a decade
B - so in being the lowest in a decade
C - to the lowest level in a decade
D - to what would be the lowest in a decade
E - to a decade-low level

Can someone please explain this question?

OA : C