Question

他們看上去這樣蒼老，那是因?yàn)樗麄冊��?jīng)辛辛苦苦地勞動(dòng)了十年。

Answer 1

They looked so old.That's ?because? they had worked hard for ten years.

 

表語從句，如果從句表原因，則用because 引導(dǎo)。