1. I spent 4 hours reading the first chapter of the book.

2. Tennis isn't so dangerous as snowboarding.

3. They're not sure how to operate the new system.

4. He said: "I will not have enough time to finish the job".

1. I spent 4 hours (on) reading the first chapter of the book.

-> S + spend/ waste + time/money + (on) + N/ doing sth: dành/ lãng phí thời gian/ tiền bạc vào việc gì/ cái gì.

2. Tennis is not as dangerous as snowboarding.

-> S + be (not) + as + adj + as + O: cái gì (không) bằng cái gì (so sánh ngang bằng)

3. They're not sure how to operate the new system.

-> how to do sth: biết làm gì.

4. "I will not have enough time to finish the job", he said.

-> chuyển từ câu gián tiếp sang câu trực tiếp.