A) and D) don't fit: "as" and "such as" don't work in that context.
E) doesn't fit: "the slower" is a noun phrase.
That leaves us with choices B) and D), both of which sound awkward to my ears. But let's look at the grammar anyway:
C) the most slowly/the more
"slower" is a comparative; e.g., ... is increasing slower than ..., whereas "the most slowly" doesn't require "than"; e.g., the most slowly increasing ... / ... increasing the most slowly.
All the best.
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