The US warns al-Qaeda may be planning an attack in Yemen's capital, where the US and UK embassies _______ shut.
b) have been
Please, could you tell which one is right and why?
Thank you so much.
"Have been shut" is correct, it means that at some time in the recent past they were closed and they remain closed at the moment. If you use "were" it means that in the past they were closed, it doesn't say whether or not they are closed now.