You are allowed to attend any lecture, only if there are empty seats for you and you don't disturb the class.

只要教室里还有空位，你又不扰乱课堂，你就可以旁听任何课。

youdao

The value of the remaining letters written in the a | a format. If there are no letters left, the value is empty; otherwise, you call the template recursively.

用a | a格式写的剩余字母的值如果已没有字母，则该值为空；否则，递归调用该模板。

youdao

The other unused entry points, if any, are automatically mapped to empty functions, thus there is no need to use Adapter classes.

其他未使用的入口点(如果有的话)自动映射到空函数，因此这里不需要使用Adapter类。

youdao

That means houses and neighborhoods remain empty even if there are buyers ready, willing and able to do so.

WHITEHOUSE: Press Briefing