Questions & Answers about Compré un kilo de sardinas por cinco euros.
Why is por used here instead of para?
This is a classic rule for choosing between the two! Use por whenever you are talking about an exchange, such as paying a specific price for a product. Since you are exchanging five euros for the sardines, por is the correct choice.
Why use the past tense compré here instead of compraba?
The preteritetense (compré) is used for actions that are viewed as a single, completed event in the past. Buying the sardines happened once and was finished. If you used the imperfect tense (compraba), it would describe a past habit, meaning 'I used to buy a kilo of sardines for five euros.'
Why is there a de between un kilo and sardinas?
Whenever you use a noun that measures a quantity (like un kilo, un litro, or una taza), you must connect it to the item being measured with de. Just like in English, it translates literally to 'a kilo of sardines'.