Hi !!
1- The town wouldn't have been destroyed if the volcano hadn't been so destructive.
2- If the inhabitants had evacuated early enough, the terrible disaster wouldn't have been averted.
3- If the weather is gloomy, we will stay in the hotel and read.
4- If heard a loud, ......, I would return to the hotel immediately.
5- A tsunami would be set off if a nearly volcano erupted.
Explanation
if + present ---------> main clause = future
if + simple past ---> main clause = would
if + past perfect ----> main clause = would have
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