They have been to UK twice.
一般问句 Have they been to UK twice ？
特殊问句 Where have they been to twice ？
或 How many times have they been to UK?
或 Who have been to UK twice ？
现在完成时一般疑问句和特殊疑问句造句
They have been to UK twice.
一般问句 Have they been to UK twice ？
特殊问句 Where have they been to twice ？
或 How many times have they been to UK?
或 Who have been to UK twice ？