It was written in old English
Since a participle takes the form: verb + -ing, the only word in this sentence which has such a form is B, 'challenging'. 'Puzzle' is a noun, 'crossword' is an adjective, 'created' is a verb.
D and B to some extent are the same things that come with each other.
For most, B.
I think the answer is C but that’s just a guess
Nucleus is the cell structure contains informations needed for protein synthesis
