| 都表“过去”，有时间先后之分也有强调的不同点 |
| 过去完成时(过去的过去 + 强调结果) |
had + done |
A short time before, great trees had covered the countryside.. |
| 过去完成进行时(过去的过去 + 强调过程) |
had been + doing |
Firemen had been fighting the forest for nearly three weeks.. |
| 一般过去时(无强调) |
did |
Now, smoke still rose up from the warm.. |
| 过去进行时（过去正在进行） |
was/were + doing |
Winter was coming on and the hills threatened the surrounding villages with destruction... |
| 过去将来时(过去的之后) |
would + do |
for heavy rain would not only wash away the soil but would cause serious floods as well. |
