It is hardly possible that I can get there by six.
６時までにそこに着くのは不可能に近い
It is held to be good for the health.
それは健康によいと考えられている
It is highly desirable that you (should) get there by tomorrow.
明日までにそこに着くのが大変望ましい
It is highly improbable that she will marry him.
彼女が彼と結婚するなんてとうていありえない
It is highly unlikely that such an accident could occur.
そのような事故が起こることはとうていありえない
It is hopeless to continue trying to convince him.
彼に納得させようとし続けてもむだだ
It is I.
それは私です（◆((略式))では通例It's me. 詠嘆の表現などでもIの代わりにmeが用いられる：Dear me!おや，まあ）
It is illegal to discriminate on the basis [grounds] of sex.
性差別は違法だ
It is illegal to do ...
…することは不法である
It is immediately obvious that ....
…ということはただちに明らかとなる
