Which one of following changes would result in greatest increase in reaction rate in the following two-step mechanism?

Question

Step (i):$NO_2(g)+NO_2(g)\rightarrow NO(g)+NO_3(g)$[slow].

Step(ii):$NO_3(g)+CO(g)\rightarrow CO_2(g)+NO_2(g)$[fast).

$\begin{array}{1 1}(a)\;increase \;[CO]\\(b)\;increase\; [NO_2]\\(c)\;decrease\;[NO]\\(d)\;decrease\;[NO_3]\end{array}$