he knew he could not finish his homework ___ .a.before his parents cameb.until his parents have come c.by his parents came d.when his parents come写出原因!

he knew he could not finish his homework ___ .a.before his parents cameb.until his parents have come c.by his parents came d.when his parents come写出原因!
he knew he could not finish his homework ___ .
a.before his parents came
b.until his parents have come
c.by his parents came
d.when his parents come
写出原因!

he knew he could not finish his homework ___ .a.before his parents cameb.until his parents have come c.by his parents came d.when his parents come写出原因!
选b.他知道直到父母回来他才能完成作业.首先排除第三个,by 后面应该是名词或动名词,第四个也不对,语意不通.剩下的两个,由于主语是过去时knew,那么后面的时态应该是更加过去的时态,因为那是他knew的内容,于是选第二个.

C他知道在父母亲回来之前，他是完不成任务的

选B
not until 直到……才

选A。意思是；他知道在父母回来前无法完成作业了。时态与主句一致，都为过去时。我只能这么说了

B 直到...才...
词典例句千万不要随便说“Oh,my God！” Why？！ 1. It was not until his third match in 1790 that he finally beat Humphries and become Champion of England.
直到1790年第三次比赛时，他才最后打败汉弗莱斯，而成为英国的冠军。
来自《...

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B 直到...才...
词典例句千万不要随便说“Oh,my God！” Why？！ 1. It was not until his third match in 1790 that he finally beat Humphries and become Champion of England.
直到1790年第三次比赛时，他才最后打败汉弗莱斯，而成为英国的冠军。
来自《用法词典》
2. It was not until yesterday that I learned it.
顶昨天我才听说这件事。
来自《现代汉英综合大词典》
3. It was not until yesterday that I noticed it.
直到昨天我才注意到这件事。
来自《现代英汉综合大词典》
4. Not until last week was the project in full blast.
工程直到上星期才全部开工。
来自《简明英汉词典》
5. People say: "Guilin's scenery is peerless in the world." It was not until I visited the place that I found it really worthy of the reputation.
人们都说“桂林山水甲天下”， 到桂林一看，果然名不虚传。
来自《现代汉英综合大词典》
6. Block-printed books did not appear until the Song Dynasty.
及至宋代，方有刻本。
来自《现代汉英综合大词典》
7. Do not permit children to indulge in superfluities until esqsentials are met.
在孩子们未抓住要点之前别让他们过于注意细节。
来自《现代英汉综合大词典》
8. Do not sell on any account until further advice.
在另行通知前切勿出售。
来自《简明英汉词典》
9. Feudalism was not abolished in England until 1660.
英国直到1660年才废除封建制度。
来自《简明英汉词典》
10. He chose not to go home until later.
他决定晚一点回家。
来自《简明英汉词典》
11. He did not agree until I had talked to him for a long time.
我劝说了半天，他才肯了。
来自《现代汉英综合大词典》
12. He did not go until night.
他直到夜里才走。
来自《现代英汉综合大词典》
13. He did not wake to the danger until he discovered that he was surrounded on all sides by the enemy.
直到发现被敌人四面包围，他才意识到自己处境十分危险。
来自《简明英汉词典》
14. He will not lay it down until it is finished.
他没干完的事决不会放下不干。
来自《现代汉英综合大词典》
15. His fame as a poet did not come until after his death.
他死后才获得诗人的名声。
来自《现代汉英综合大词典》
16. John did not like his job, but he decided to hang on to it until he found a better one.
约翰不喜欢他的工作，但他决定干下去，直到找到更好的工作。
来自《简明英汉词典》
17. Smith's report was not officially okayed by the War Department for Release until July 9.
史密斯的报告于7月9日才获得释放战俘处正式批准。
来自《简明英汉词典》
18. The airport did not become operational until May.
机场到五月才可以使用
19. The bolt is worn and not an exact fit but it will serve its turn until I can buy a new one.
这个螺栓已经坏了，不能拧紧了，但在我还未买来新的之前暂时再用一下。
20. The children are not allowed in until the school bell rings, whatever the weather.
无论什么天气，铃响之后才能允许学生们进学校

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