If l₁ and l₂ are the length of the first and second resonating air columns in a resonance tube then the
A - Ratio of l₁ to l₂ is 1 : 2
B - Ratio of l₁ to l₂ is 2 : 1
C - Difference of l₁ and l₂ is λ/2
D - Sum of l₁ and l₂ is λ/2