重点讲解：
1. convert into (使)改变；更改；(使)转变；
Convert food into absorbable substances.
把食物转化为可吸收的物质。
2. in operation 使用；运作；
The new machine is now in operation.
新机器已经开始使用。
3. on board 在火车（或轮船、飞机）上；
The cargo on board have been damaged by sea water.
船上的货物因水湿而残损。
4. come down with 染上，得了(病)；
I feel dizzy and suffocated. I think I have come down with heatstroke.
我感到头晕，喘不上气来。我想是中暑了。