2018高考二輪復習英語教案: 介詞和連詞
2、before作連詞一般表示時間，意為“在…之前”，但有些句子中這樣譯就顯得別扭。試看以下句子的翻譯：he almost knocked me down before he saw me.他幾乎把我撞倒才看見我；before i could get in a word he had measured me.我還沒來得及插話，他已經給我量好了尺寸
3、till, until作為介詞式從屬連詞引導時間狀語短語或狀語從句，用于否定句時，結構為not …until (till)，主句謂語動詞延續與非延續皆可，意為“直到…才…”。用于肯定句時，只與延續性動詞連用，表示“到…為止”。例如：they played volleyball until (till) it got dark./ they didn’t talk（延續性動詞）until (till) the interpreter（譯員）came./ he didn’t go to bed（非延續性動詞）until (till) the his father came back.；until可以放在句首，till則不行，例如：until the last minute of the match we kept on playing./ not until he finished his work did he go home.（倒裝）；till, until只用于時間，以下句子是錯誤的：we walked till the edge of the forest.（要用as far as或to）
4、because, since, as引導原因狀語時注意使用上的區別：①如果原因構成句子的最主要部分,一般用because ,因此because引導的從句往往放在句末。用why提問的句子，一定用because回答。例如：he had to stay at home yesterday because he was ill.；②如原因已為人們所知，或不如句子的其他部分重要，就用as，或 since。since比as更正式些。as和since引導的從句一般放在句子的開頭。例如：as you are tired, you had better rest./ since everyone is here, now let’s begin
5、although和though引導讓步狀語從句往往用法一樣，但注意以下區別：
①although用于各種文體，而though則多用于非正式的口語或書面語中。注意由although, though引導的從句后，主句不能用but，但可用副詞yet, still。例如：although/ though it rained all the morning, they still went on working.（或yet they went on working）
②though常與even連用，even though表示強調，意為“即使”，但不能說even although，例如：even though i didn’t understand a word, i dept smiling.
③though可用作副詞，意為“然而”，常用逗號與句子分開。although則不能這樣使用，它只作連詞。例如：it was a quiet party, i had a good time, though.
6、once作副詞譯“曾經”，作為連詞譯“一旦”，引導條件狀語從句。相當于if的加強形式。例如：i don’t believe he was once a thief. (once這里是副詞)/ once aristotle had made up his mind that heavy objects always fell faster than light objects, he taught it as a truth to his students. (once連詞)
7、unless引導條件狀語從句等于if … not …。例如：he’ll accept the job unless the salary is too low. ( = he’ll accept the job if the salary is not too low.)
8、在用as if引導的方式狀語從句及表語從句中，根據情況要使用虛擬語氣。例如：he talks as if he knew all about it. 但有時也可用直陳語氣。例如：it looks as if it is going to rain.