My teacher gave me an exercise which is adapted from the book "Macmillan Advanced Language Practice with key"
Complete the second sentence so that it has a similar meaning to the first sentence, using the word given. Do not change the word given.
(a-1) Tony knew what the answer was after reading the book. (read)
(a-2) By the time Tony ____________.(Adapted) Source: https://studfiles.net/preview/1462020/page:19/
I understand the sentence a-1 as: First, Tony read the book. Then, he knew the answer.
So, my rewrite in sentence a-2 is:
By the time Tony knew what the answer was, he had read the book.
However, when I checked the book's answer key, it said:
By the time Tony had read the book, he knew what the answer was.
I seem not to agree with the book's solution, because I understand that "by the time" means "earlier than or equal to the time"; as a result, for me, the meaning of the book's solution is that first, Tony knew the answer, then he read the book. And it isn't similar in meaning to the original sentence.
Could you kindly tell me whether I correctly understand the meaning of the book's solution?
Best Answer
While your answer is grammatically correct, it's not logical. When you use the expression "By the time X happened, Y happened" the focus is on Y, not X. This establishes some kind of significant relationship between X and Y, and provides a time frame for when Y occurred.
In this example, we are more concerned about the criminals getting away than the police arriving. If you reverse the order, it doesn't really make sense:
Here the focus changes to when the police arrived, which seems odd, because there is no significant relationship between the criminals escaping and then the police arriving. One didn't cause or affect the other.
That being said, your confusion is justified, because the exercise is flawed:
First, Tony read the book, and then, after he was done, he knew the answer. Yes, of course Tony had been figuring out the answer while he read the book. But the sentence itself is very clear about when he was certain of the answer.
There really is no 100% correct way to rephrase this starting with "By the time". I would imagine any other examples from the site you link may be equally suspect.