The correct option is B many
Let’s examine the sentence: “If we are to write any article for the magazine, we must necessarily read ____(39)____ new books.” The sentence needs an adjective of number for books. Option A cannot be used as ‘minimum’ means ‘in the least quantity’ and this does not fit in with the sense of the sentence. Same goes for Options B and D. Moreover, Options B and D are used for uncountable nouns and ‘books’ indicate countable noun. Hence, option C is the correct answer.