Anadiplosis is a rhetorical device where the last word or phrase of one sentence or clause is repeated at the beginning of the next.
In the examples you provided, the sentence that demonstrates anadiplosis is:
"A book is a key. It opens a world of wonder. It unlocks ideas for which the mind hungers. With a book, one can enter a new world."
Here, the word "book" is repeated.
However, none of the options perfectly illustrate anadiplosis as traditionally defined, where the final word or phrase of one clause leads directly into the next clause. The closest example might suggest some familiarity, but a more precise example would be: "Fear leads to anger; anger leads to hate; hate leads to suffering."
If you're looking for a better illustration of anadiplosis, you might want to replace one of the sentences with a more direct example.