快速答案
reservar 预留未来可用性；alugar 付费取得临时使用权。
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
alugar
to rent
Use alugar for paying for temporary use of a home, vehicle, equipment, or other property.
reservar
to reserve or book
Use reservar for holding a room, table, seat, or service for later use.
如何选择
- alugar: Choose alugar if the sentence points to paying for temporary use of a home, vehicle, equipment, or other property.
- reservar: Choose reservar if the sentence points to holding a room, table, seat, or service for later use.
例句
Alugamos um carro por três dias.
We rented a car for three days.
Reservei um quarto para sexta-feira.
I booked a room for Friday.
常见误区
You may reservar a car before the trip and alugar it when the rental begins. The booking is not the rental itself.
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 alugar，一次用 reservar。如果两个版本都可以，说明意思怎样变化。