The percentage increase in imports over the previous year is maximum during

The percentage increase in imports for each given option using the formula: $\frac{\text{New Value - Original Value}}{\text{Original Value}} \times 100$

2009 to 2010:

Imports 2009: $280$

Imports 2010: $310$

Percentage increase = $\frac{310 - 280}{280} \times 100 = \frac{30}{280} \times 100 = 10.71\%$

2010 to 2011:

Imports 2010: $310$

Imports 2011: $290$

This is a decrease: $\frac{290 - 310}{310} \times 100 = -6.45\%$

2013 to 2014:

Imports 2013: $300$

Imports 2014: $320$

Percentage increase = $\frac{320 - 300}{300} \times 100 = \frac{20}{300} \times 100 = 6.67\%$

2008 to 2009:

Imports 2008: $260$

Imports 2009: $280$

Percentage increase = $\frac{280 - 260}{260} \times 100 = \frac{20}{260} \times 100 = 7.69\%$

Comparing all values, the maximum percentage increase was $10.71\%$ during 2009 to 2010, making this the correct answer.