今天讲试卷讲到他们的爱好是集邮。 不知道该如何翻译：
Their hobby is collecting stamps. 还是 Their hobbies are collecting stamps.或是 Their hobbies is collecting stamps.请教了

Their hobby is collecting stamps.

Their hobby is collecting stamps. 同一个爱好就是单数啦

Their hobby is collecting stamps.
第三种说法肯定不对的。