The Following Table Identifies the Real Value of Exports, Imports

The following table identifies the real value of exports, imports, and gross domestic product GDP) for a country for three different years, measured in billions of dollars. $$\begin{array} { l l l l } \hline \text { Year } & \text { Exports } & \text { Imports } & \text { GDP } \\\hline 1990 & 434.00 & 400.00 & 2,170.00 \\2000 & 499.10 & 480.00 & 2,712.50 \\2010 & 459.01 & 560.00 & 3,255.00 \\\hline\end{array}$$
a. During this time period, what has happened to exports and imports as a percentage of GDP? Calculate the values.
b. During this time period, what has happened to the trade balance? Calculate the values.
c. Provide a plausible explanation for why the values might have changed in the way they did.