Non-specific time reference
1. In recent years, there has been a dramatic increase in the percentage of bilinguals in population.
2. In recent years, there was a dramatic increase in the percentage of bilinguals in population.
Specific time reference
3. During the 1990's, there was a steep rise in the proportion of Europeans using mobile phones.
The beauty of the present perfect is that it places focus on the event, not when that event happened. Which is why specific time adverbial (e.g., yesterday, 4 o'clock) aren't compatible with the present perfect."The following words are often used with the present perfect: since, for, recent, recently, just, ever, yet, already."Use the simple past with specific time adverbials.
The present perfect tense
Student or Learner