7. 某些主语从句中的谓语动词要用虚拟语气
　　某些表示命令，要求，决定，建议，主张以及“重要性”和“紧迫性”等概念的主语从句中谓语动词要用虚拟语气。这时，谓语动词用动词原形或should +动词原形。这类主语从句一般由 “It is (was) + 形容词/过去分词 + that引导的从句”构成。该结构中，常用的形容词主要有：advisable, appropriate, desirable, essential, imperative, important, necessary, obligatory, proper, urgent, vital等;常用的过去分词主要有：arranged, decided, demanded, desired, ordered, proposed, recommended, requested, suggested等。

　　It is necessary that you (should) stop smoking so heavily.
　　It is arranged that you (should) enter for this competition.