Dưới đây là cách viết lại các câu trên: 1. In 2015, there was a significant drop to 20% in the number of people watching films on TV. 2. In 2010, privately rented homes experienced a quick 10% increase. 3. The average length of the advertisement saw a moderate increase of 30 seconds in 2009. 4. There was a steady increase of $2 million in salt exports in 2017. 5. Over the period, the price of computers showed a gradual decrease. 6. In 2014, the number of visitors to Hanoi showed an upward trend. 7. Throughout the period, the number of students studying two languages stayed stable. 8. In 2017, history book sales experienced a sharp 20% decline. 9. In 2009, there was a slight improvement in the quality of supermarket food. 10. Between 1990 and 2000, the percentage of smokers saw a remarkable decrease of 35%. 11. In 1979, there was a 30% increase in the number of heaters in households. 12. The number of engineering degrees saw a noticeable drop in 2014. 13. In December, iced coffee sales significantly increased to around 40 servings per day.