Answer:
(1) An author doing research for a book asked thousands of Americans what made them happy.
Explanation:
It's tempting to say that the main idea is the conclusion of the paragraph, which is stated in sentence (5). However, the main focus of the paragraph is more on the research on what makes American happy, which is detailed by the responses of the research subjects, as well as the conclusion of the research study. If (5) was the main focus, there would be more details about why most of the things that make you happy are simple and free or inexpensive or what the general research about this topic has been, instead of just one study in particular.
The text:
__________
"Then he began teaching at Pinkerton Academy."
__________
is NOT a "run-on" or "sentence fragment"; rather, it is a complete sentence.
The ship was not abandoned by the sailors.
