If you say that something is ~, you are emphasizing that it is true and cannot be shown to be untrue.
It is ~ that birds in the UK are harbouring this illness...
= undeniable
ADJ: oft it v-link ADJ that emphasis
If you say that something is ~, you are emphasizing that it is true and cannot be shown to be untrue.
It is ~ that birds in the UK are harbouring this illness...
= undeniable
ADJ: oft it v-link ADJ that emphasis
Collins COBUILD. Толковый словарь английского языка для изучающих язык Коллинз COBUILD (международная база данных языков Бирмингемского университета) . 2012