The correct answers are:
b. new interest in mining for gold and silver;
The people in Southeast Asia have kind of stopped with the mining of gold and silver for few centuries, even though until the 14th century there was a lot of mining of this two precious metals. The French changed that, and they encouraged, or rather forced, the mining of the gold and silver again, which brought them a lot of wealth.
d. establishment of plantations;
The climate in Southeast Asia is very suitable for certain types of crops and trees, so the French used that. They established a lot of large plantations and made the locals work on them, giving them enough payment just to be able to survive.
