20.
Your Answer is
Correct Answer is G
Explanation
G item: Here it means "entering the darkest place from a small fissure". The most correct word order is G item.
F/J item: here i had even seen to modify darkness, so F/J item is wrong.
Item H: blackest modifies darkness, so item H is wrong, and in item H, slight and blackest conflict, they cannot be put together, and item H is wrong.