单选题 They left at nine, so they ______ by now.
【正确答案】 C
【答案解析】[解析] should have arrived by now“现在应该已经到达了”。should have done用于判断,表示说话时某人应该已经做了某事。也可表示“本来应该已经做了某事”(但实际上并未做),含有责备之意。