What is the correct answer?
4
A. (td₁ -td₃)/( td₂ -td₃)
B. (td₂ -td₃)/( td₁ -td₃)
C. (td₃ -td₁)/( td₂ -td₃)
D. (td₃ -td₂)/( td₁ -td₃)