Demands differ from wants because:. a. demands are unlimited, whereas wants are limited by income.
b. wants require a plan to acquire a good but demands require no such plan.
c. wants imply a decision about which demands to satisfy, while demands involve no specific plan to acquire the good.
d. demands reflect a decision about which wants to satisfy and a plan to buy the good, while wants are unlimited and involve no specific plan to acquire the good.

The correct answer is:

demands reflect a decision about which wants to satisfy and a plan to buy the good, while wants are unlimited and involve no specific plan to acquire the good. (d)

Explanation:

Let me first try to define what demand and want are:

want: want is a desire for a product or service. It is said that wants are unlimited, however, the resources to actualize such wants are in a limited supply.

Demand: Demand is the quantity of good or service that a person is willing and able to pay for because of the availability of resources to do so, at a given price and time.

For a clearer understanding, demand can be seen as a subset of want that a consumer takes a further step to acquire, not just desire. There is a specific plan to acquire such wants.

b. take periodic breaks and alternate between tasks.  

will increase work efficiency, and avoid health issues.