快速答案
rua 泛指城市街道；avenida 通常是更宽或更主要的城市道路。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
rua
street
Use rua for the general urban road and the default word in addresses.
avenida
avenue
Use avenida for typically a larger or more important urban road.
如何选择
- rua: Choose rua if the sentence points to the general urban road and the default word in addresses.
- avenida: Choose avenida if the sentence points to typically a larger or more important urban road.
例句
Moro numa rua tranquila.
I live on a quiet street.
O ônibus passa pela avenida principal.
The bus goes along the main avenue.
常见误区
Official names decide the label. A road called Avenida can be small, so copy the address rather than reclassifying it.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 rua，一次用 avenida。如果两个版本都可以，说明意思怎样变化。