参考答案

正确答案：A
解析：考查虚拟语气。It is imperative that结构中需用“(should)+动词原形”虚拟语气，因此正确答案为should return。这类形容词包括：advisable, anxious, better, concerned, desirable, eager, essential, fair(=just), good(=just), imperative, important, just, mandatory, natural, necessary, obligatory, proper, reasonable, right, urgent, vital, wrong, no wonder(名词)。