What's the difference between using a search folder and using the search field?

a. A search folder and its results are always available, but search field results are designed to be temporary.

b. There is no difference between using a search folder and using the search field.

c. A search folder only searches for items within the selected folder whereas the search field can contain items from any element in outlook.

d. The search field only searches for items within that element whereas a search folder can contain items from any element in Outlook.