<p dir="ltr"><span><span>This question is a complex sentence. The main clause is “_______ discussing matters </span></span>that are irrelevant to the topic,” preceded by an adverbial phrase “When making a presentation in the seminar”.</p><p dir="ltr"><span><span>Let’s look at the main clause: </span></span></p><p dir="ltr"><span><span>“</span></span>_______ discussing matters that are irrelevant to the topic<span><span>” </span></span></p><p dir="ltr">The blank should be filled with a subject and a verb for the clause. However, all four choices don't have a subject. </p><p dir="ltr">In most cases, an English sentence should have at least one subject, but there are exceptions: imperative sentences. An imperative sentence directly starts with the basic form of a verb, with the implied subject “you” omitted. </p><p dir="ltr">Thus, the main clause should be an imperative sentence, and the blank should be filled with the basic form of a verb. Thus, the correct answer is the basic form of a verb, (D) avoid.</p>