解題之前,先來了解下can,could 和 be able to三者的區(qū)別與聯(lián)系.
1.can的過去式是could,但could 除了可作can的過去式外,還可表比can更委婉的語氣,因此在回答由could 表示請(qǐng)求的問句中,不能用could,但可用can.如：
—Could you lend me a hand?
—Of course I can.
2.在表示現(xiàn)在或過去的智力、體力、技能等方面的“能力”時(shí),can,could ?？膳cbe able to互換.如：
He could (or was able to) swim five miles when he was a boy.
3.be able to比can有更多的表現(xiàn)形式,如"will be able to","have (has) been able to" "had been able to" 等等.因此be able to常被用來表示can所不能表示的將來或完成的概念.如：
They will be able to run this machine on their own in three months.他們過三個(gè)月就能自己開這臺(tái)機(jī)器了.
4.在表示成功地做了某事時(shí),不用could,而用was / were able to (或managed to,succeeded in doing sth )來表示.如：
He was able to (or managed to) finish the job yesterday.
但是couldn't和wasn't / weren't able to ?？苫Q.如：
I couldn't / wasn't able to finish the job yesterday.
5.與感覺動(dòng)詞連用時(shí),can,could亦可與be able to互換.如：
We could/were able to smell something burning in the kitchen.
選項(xiàng)B was able to是過去時(shí) 而題中所問對(duì)象還未成功完成某事,所以不用過去時(shí)態(tài),不符合題意,故B可以排除.
選項(xiàng)D would 先了解下它的用法與意義
1.will的過去式.
例：They said it would be fine.聽說天氣會(huì)很好.（it will be fine的過去式）
例：I said I do my best.我表示過要盡最大的努力.
2.（在陳述語氣中,表示過去將來時(shí),表示無意識(shí)的行動(dòng)或單純將來發(fā)生的事或動(dòng)作,指實(shí)際情況,一般用于間接引語中）會(huì)；將；
例：he said he not be free that night.他說他那天晚上沒有空.
所以 would be able to 是過去將來時(shí)態(tài) 不符合題意
因此選C
Could you please tell me if he is able to finish the work on time
你能告訴我他是否能夠按時(shí)完成這項(xiàng)工作嗎?