Abusiness chooses to build army tanks rather than butter-making machines. what is this called?
a. factors of production
b. trade-off
c. scarcity.
d. none of the above

This would be called a trade-of B. 

The reason why this is correct is because if you can only build one thing as a company and you decide that building war equipment is more important to you, then you're doing a trade-off between building butter-making machines and army tanks.