The correct answer is (a).
The combined share of exports and imports of goods was 14.2 percent of GDP in 1990-91. In 2011-12 this share became 46.4 percent of GDP. This means that the share of exports and imports of goods in GDP increased by 32.2 percentage points from 1990-91 to 2011-12. This is equivalent to an increase of almost two times.
Option (b) is incorrect because the share of exports and imports of goods in GDP increased by 32.2 percentage points, not 30 percentage points.
Option (c) is incorrect because the share of exports and imports of goods in GDP increased by 32.2 percentage points, not 50 percentage points.
Option (d) is incorrect because the share of exports and imports of goods in GDP increased by 32.2 percentage points, not 100 percentage points.