26.
(A) If it were not
(B) If it had been
(C) Should it be
(D) Had it not been

• If I were you, I wouldn’t do that.
  = Were I you, I wouldn’t do that. (如果我是你，就不會那麼做了)
• If he had taken my advice, he might not have made such a bad mistake.
  = Had he taken my advice, he might not have made such a bad mistake. (要是他聽我的勸告，就不會犯這樣嚴重的錯誤了)
• If I should have a chance to try it, I would do it in another way.
  = Should I have a chance to try it, I would do it in another way. (要是我有機會試一試，我會用另一種方法去做) — Should 係表示有機會一試的可能性微乎其微。
• If we were to have children, we’d need to move to a bigger house.
  = Were we to have children, we’d need to move to a bigger house. (如果/要是將來有小孩，我們必須換一間較大的房子) –「were to + 原形動詞」是另一種與未來事實相反的條件句型。

如果條件句為否定形式，那麼在寫成