我們認為選A和B均可以。但意思稍有不同：　　

■如果選A　　

If you hadn't taken such a long time to get dressed, we would be there by now. 的意思是：你要是沒花那么長的時間穿衣服的話，我們現在就會到那兒了。　　

類似例句：　　

They must have gotten lost or they’d be here by now. 他們一定是迷路了，否則現在他們應該到了。——摘自《麥克米倫高級英語詞典》must 詞條。（句中的 or 相當于：If they hadn’t gotten lost. 即原句相當于：They must have gotten lost. If they hadn’t gotten lost, they’d be here by now.）　　

If you’d got on with your work instead of wasting time chatting, you’d be finished by now. 你是要是不停地繼續你的工作，而不是浪費時間去閑聊，到現在你就做完了。——摘自《劍橋高級英漢雙解詞典》第三版time詞條　　

■如果選B　　

If you hadn't taken such a long time to get dressed, we would have been there by now. 的意思是：你要是沒花那么長的時間穿衣服的話，我們現在就會已經到那兒了（或早就到那兒了）。　　

類似例句：　　

They would have been here by now if they’d caught the early train. 他們要是趕上了早班火車，現在早都該到這兒了。——摘自《牛津高階英漢雙解詞典》第六版 if 詞條　　

If they’d operated and pinned her arm at once, she might have healed by now. 如果他們當時馬上就給她的胳膊做手術并用鋼針固定，她現在可能已經痊愈了。——摘自《柯林斯高級英語詞典》heal 詞條