Breakdown of Tu as répondu au message de ta copine ?
tu
you (informal singular)
avoir
to have
le message
the message
de
of / from / any (in negative sentences) / about (concerning)
Questions & Answers about Tu as répondu au message de ta copine ?
Why does répondu end in an -u?
This sentence is in the passé composé (a past tense). To say "you replied", we use a helper verb (tu as) plus the past participle of répondre (to reply). For regular verbs ending in -re, you drop the -re and add -u. So, répondre becomes répondu.
Why is it au message instead of just le message?
How does de ta copine translate to "your friend's"?
French doesn't use an apostrophe-s ('s) for possession. Instead, you have to use the word de (of) and phrase it as "the message of your friend". So, au message de ta copine literally means "to the message of your friend".
Why isn't there a word for "Did" at the beginning of the question?