7. He has set his heart on becoming a doctor.
Explanation: "He is determined" means he has a strong desire or goal. "To become a doctor" is the objective he is determined to achieve. "Set one's heart on" is an idiom that means to have a strong desire or determination for something.

8. I expect the book to be short of far better because it had been written by such a good novelist.
Explanation: "I expect" means I anticipate or believe. "The book to be far better" means I believe the book will be of higher quality or more enjoyable. "Because it had been written by such a good novelist" explains the reason for the expectation. "Short of" means lacking or not reaching a certain level, so the sentence doesn't make sense with this word.

9. He never felt so timeless when he looked at a picture.
Explanation: "He never felt so emotional" means he has never experienced such strong emotions. "When he looked at a picture" explains the situation in which he felt emotional. "Timeless" means without a sense of time or eternal. However, it doesn't fit in the context of the sentence, as it doesn't convey the intended meaning.

10. I'm rather keen on silver, I much prefer it to gold.
Explanation: "I'm not very keen on gold" means I'm not very interested or enthusiastic about gold. "I much prefer silver" means I have a strong preference for silver. "Rather" is used to emphasize the preference for silver over gold.