Given the following two mechanisms, one with catalyst and the other without catalyst.
(i) `A + B rarr C` (slow)
(ii) `C +B rarr F + A` (fast)
(iii) `B + B rarr F` (slow)
Which mechanism use the catalyst and what is it ?
A. Step (i), `A`
B. Step (ii), `B`
C. Step (iii), `F`
D. Steps (i) and (ii), `C`