难怪他没来，原来他生病了。
nánguài tā méi lái ， yuánlái tā shēngbìng le 。
No wonder he didn't come: he's ill.
难怪外面这么热闹，原来今天过节。
nánguài wàimiàn zhème rènao ， yuánlái jīntiān guòjié 。
No wonder it's so lively outside: today's a festival.
难怪房间这么干净，原来你打扫过了。
nánguài fángjiān zhème gānjìng ， yuánlái nǐ dǎsǎo guo le 。
No wonder the room is so clean: you've cleaned it.