Which sentence is correctly capitalized? A. It was President Abraham Lincoln who was in power during the
American Civil War.
B. It's New York, so there is always something to do in the City.
C. In late Summer, we should visit the arboretum to see the flowers
in bloom.
D. The Dog I love most is the German Shepherd.

a

explanation:

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.