1. He became interested in two theories that possibly explained how cholera killed people.
2. He was determined to find out why.
3. ①Worried about the journey, I was unsettled for the first few days.
②Given better attention, the trees could grow better.
③Described as an enormous round plate, it spins slowly in space to imitate the pull of the earth’s gravity.
4. ①Hit by a lack of fresh air, my head ached.
= Because I was hit by a lack of fresh air, my head ached.
②I stared at the moving model of the waste machine, absorbed by its efficiency.
=I stared at the moving model of the waste machine, and was absorbed by its efficiency.
