D. by improving agriculture is the correct answer.
Explanation:
Vietnam improve its economy in the late 1900s by improving agriculture by improving agriculture and by growing the good quality of crops vietnam improve its economy.
Vietnam is the hub of the food processing that works to fulfill the high demand for food from both the local and global markets
Rice is the major crop grown in Vietnam it grown in a Red and Mekong river deltas and also other major crops such as cassava, nuts, sugarcane, corn, and sweet potatoes.
by providing a good quality of food its demand gets increased and this made the rise and improve in the economy.
