Choose the option that best completes the sentence. The lecturer insisted that every student ___ the assignment before the end of the week.

Verbs of demand such as insist, recommend, demand and require are followed by the present subjunctive, which is the base form of the verb with no -s ending. 'Every student submit' is therefore correct. 'Submits' is the common error of applying ordinary singular agreement where the subjunctive is required.