Adecimal outline is an outline that uses notations such as

A). 1.1, 1.2, and 1.3.

Explanation:

Outline, in general, is described as the series or list to exemplify the key points or topics of content or subject. There are varied types of outlines like the numeric, alpha-numeric, decimal outline, etc. that are employed for different purposes.

If decimal outline, in particular, is concerned it is employed to link each outline/point to the central content(whole) where each element contributes to accomplishing the whole. In the given question, a decimal outline would be regarded as the outline that employs numeric notations with decimals to present a complete whole by connecting each element to achieve the whole. Thus, option A is the answer as it exemplifies decimal notations.

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.

the answer is camped