When to remove scale from the cooling spaces， acid solution （） in the system can be tested from time to time by putting some on to a piece of lime.
举一反三
- Acid solution（） in the system can be tested from time to time by putting some on to a piece of lime.
- It is necessary to remove （） from the cooling spaces.
- In the second paragraph, the author tells us that ______. A: a better explanation of the great issue of our time has some advantages B: nonspecialists can get help from studying in colleges and universities C: education system will benefit from the research of the great issue of our time D: all of the above
- A writer can change the point of view from time to time in the narration.
- Can you a time when the area where you live was very different from what it is today?