What is a trade-off? decreasing the amount of resources spent on all wants to reduce the total costs in future replacing one resource with another resource to satisfy a want organizing the use of a resource in a manner that fulfills all wants reducing the amount of resources spent on one want to spend more on another want

The correct answer is D) reducing the amount of resources spent on one want to spend more on another want

B) is a tempting answer, because it involves reducing one thing to increase another thing but remember that we are interested in satisfying our want, which comes from a good, not from the resource. 

A tradeoff involves how you spend your finite resources on goods that provide utility, or satisfy your want.

In the PPC (Production Possibilities Frontier), there is a tradeoff between what goods to produce, subject to finite resources. One is not choosing between resources, such as time or material inputs, these are given constraints. You choose what to use them on. 

Another example is a trip to Burger King. Choosing between a burger or chicken fingers involves a trade-off between two wants, subject to your finite resource: money. You are not reducing money to gain another resource, money is the resource and the constraint, and the tradeoff is between spending that resource on a burger or some chicken. 

Your answer would be replacing one resource with another resource to satisfy a want. Hope this helps.