Select all the statements from the "summary checking guidelines" that are true of the summary below.

For many years, scientists have tried to understand how the weak-eyed bats can travel without hitting objects. After years of experimentation, they discovered that though the bat can fly safely without sight, it needs both its mouth and its ears. Scientists found that bats send out a high pitched noise which bounces off objects and re-enters their sensitive ears. This built-in radar system enables bats to judge distances without sight.

The topic sentence includes the main idea.
The summary is clear and concise.
The summary is about one-third the length of the original.
It expresses the author's ideas and is not a private interpretation.