The correct increasing order of the acid strength of acids, butyric acid (I), 2-chlorobutyric acid (II), 3-chlorobutyric acid (III) and 2,2-dichlorobutyric acid (IV) is :
A. `IltIIltIIIltIV `
B. `IltIII lt II ltIV `
C. ` III lt II lt IV lt I `
D. `IIIltIltIIltIV`
