When to do lists are arranged in priority order they are ranked in order of

A. Difficulty

B. Convenience

C. Importance

D. Cost

The correct answer is C, Importance.

Explanation:

When to do lists are arranged in priority order, they are ranked in order of importance.

People usually make to do lists to remember the work that needs to be done by them. To do lists can be arranged in different orders according to the need of the person.

In this question, when to do lists are arranged in priority order, they are ranked in order of the importance of the task to be done.

It would probably be number C because when something is a "priority" it means how "important" something is.