It was angry that his interests were not being protected by politicians.

英訳に間違いが有れば正してください。

彼は彼の利益が政治家によって保護されていないことが腹立たしかった。
It was angry that his interests were not being protected by politicians.

ヒント
形容詞

答え ItをHeにする

He was angry that his interests were not being protected by politicians.

angryは人が主語になる形容詞