While the Empirical Studies Clearly Tell Us That Economic Growth

While the empirical studies clearly tell us that economic growth tends to be higher when a country opens its economy to international trade and international investment, these same studies:

A) have been able to help us determine exactly why this relationship occurs so persistently.
B) have not been able to help us determine why this relationship holds so persistently.
C) have also been able to prove, once and for all, that trade causes economic growth.
D) have clearly contradicted everything that trade theory and growth theory predict.