<p><span style="">The correct answer is (B) order.</span><br></p><p style="">This sentence is an example of a subjunctive mood, which is used to express hypothetical situations, recommendations, demands, uncertainty, or anything contrary to fact at present. </p><p style="">In English, the subjunctive mood is often used in that-clauses with verbs reporting a command, a wish, a necessity, or a suggestion. The structure is:</p><p style=""> "suggest/insist/recommend/demand + that + subject + base form of the verb."</p><p style="">Here's the breakdown of the sentence:</p><ol style=""><li style="">"The university" is the subject.</li><li style="">"that students order their textbooks at least a week prior to the start of the classes" is the that-clause showing what the university suggests. Notice that "order" here is in its base form, following the pattern of the subjunctive mood.</li></ol><p style="">(B) "order" is correct because it follows the rules of the subjunctive mood in English. The verb "suggest" indicates that the statement that follows is a suggestion, hence requiring the use of the base form of the verb, which is "order" in this case. The other forms "orders," "ordering," and "ordered" don't fit the structure of the subjunctive in this context.</p>