一道英语单选，为什么涉及到虚拟语气，麻烦大家帮忙看看，谢谢

涉及虚拟语气是因为demand，具体原因如下：
虚拟语气用在advice等名词后的主语从句、表语从句和同位语从句中，常用的这类名词有：advice，demand，order，necessity，resolution，decision，proposal，requirement，suggestion，idea，recommendation，preference，request，plan，motion, desire, sentence 等，谓语用动词原形或“should+动词原形”。
例如：
The demand is that manuscripts (should) be written on one side only. 按照要求，手稿单面誊写。
He issued the order that the troops (should) withdraw at once. 他命令部队马上撤退。
Their desire was that a treaty (should) be signed. 他们的愿望是签一个条约。
The sentence is that the murderer (should) be shot. 判决是杀人犯执行枪决。
We will issue the regulation that the library (should) be open even on Sunday. 我们将发布规定，图书馆即使在星期天也要开放。
It is my desire that all the members of the family (should) gather once a year. 我的愿望是，全体家庭成员每年团圆一次。