Translation:The orchestra was singing in a sweet harmony!
In response to PhilRushton: It's true language often includes a fair degree of redundancy allowing us to "understand" (guess) mis-translations. That doesn't make it correct. It is even more of a problem if people are using the courses "back to front" which I think some do ie as well as or after learning English from Romanian, they use the site as if English and learning Romanian (which I don't do but think is a good idea).
BTW having been alerted to your post, once logged on I can't see it - anyone else have that type of problem?
That opens a nice can of worms: "The orchestra were playing" vs "The orchestra was playing". Collective nouns in this situation are usually treated as singular. That would argue in favour of the "The orchestra was playing." Of course whether DL would have marked differently is anyone's guess.