Thanks, Ayuda-Tulong...
Anyway, have a look at this:
Cambridge Dictionaries Online - Cambridge University Press "The audience was/were clearly delighted with the performance."
Now, I see, it must be correct (maybe not in American English, but according to the dictionary, it must be right at least in the British English).
Are there any other (or should I say "some") words that take both singular and plural verbs?