If B ∝ C then :
C ∝ B
C ∝ 1/B
C = 1/B
C =B
If B ∝ C then we can say that B = kC (where k = non-zero constant)
⇒ C = 1k× B
1k = m ,which is another variation constant.
⇒ C = mB
⇒ C ∝ B