What is silhak?

a. the most sacred of all korean instruments
b. a truly korean style that emphasizes the study of things korean
c. a traditional korean male hat
d. the korean word for picnic

b. A truly Korean style that emphasizes the study of things Korean.

Silhak means “Practical Learning” in Korean. It is a school of thought that surged in the 18thcentury from the disagreements with Confucian teachings, a moral and metaphysical Chinese philosophy which focused on formalism and rituals, and weren't considered to be connected to the rapid changes Korea was having in matters of politics, economy, and society between the 1600s and the 1800s.

It aimed to study thing and approach to statecraft in a more practical way.  

the option which was not a function of missionaries in the northwest was the first one - they established posts for trading furs and other goods.

missionaries were sent around the world to spread religion and their knowledge and others - they were not merchants who sold furs and other goods.