Learn French: Nous aurons vendu mille tonnes de fer. - We will have sold a thousand tons of iron.

The future perfect (le futur antérieur) is formed by taking the future tense of the helping verb, which is avoir here (nous aurons), and adding the past participle of the main verb (vendu). It translates exactly to English as "will have sold".

Is vendu a regular past participle?

Yes! For regular verbs ending in -re like vendre (to sell), you form the past participle by dropping the -re and adding -u, giving you vendu.

Why isn't there a word for "a" before mille?

In French, the number 1000 is simply mille. You never put un before it the way we say "a thousand" or "one thousand" in English. Additionally, mille is invariable, meaning it never takes an "s" at the end, even if you had several thousand!

Why do we use de instead of du in tonnes de fer?

After expressions of quantity or measurements like mille tonnes, you must use a simple de (or d' before a vowel). You drop the definite article, so you don't use combinations like du or des here because the exact quantity is already specified.