The correct answer is: serious and matter-of-fact.
When writing an objective piece of writing, it is important to keep the tone formal. It should be serious and matter-of-fact so that the audience will take your topic seriously. This way, you will convey your message objectively and the audience will know that the message is important.
A gerund is a verbal that ends in -ing and functions as a noun. The one that contains a gerund functioning as a direct object is D.
The question that should you ask in order to understand an author's diction is that "<span>How has the author tried to prove a point with this argument?" This question will help the readers know what the author is trying to point out and what specific argument he is trying to work out.</span>
Stubborness or inflexibility would be appropriate synonyms for 'obstincy' as it is used in this excerpt.
Obstinacy in defence means that they are stubborn in defence - and are going to stick with it, no matter what other information comes to light.
