Identify the subject: Understanding the orbits of the stars in the sky is easy with all the benefits of modern technology, but only came about through an incredible amount of scientific labor.

At the end of the book, there was/were many lessons explained by Scout

Is the following a Sentence, Fragment, Run-on: "He was an old man who fished alone in a skiff in the Gulf Stream and he had gone eighty-four days now without taking a fish."

Although most people does/do enjoy a better standard of living today than their ancestors did, that still does not relieve us of the need for compassion today.

Each of the students who aced the final test think/thinks that it was easy, but the others think/thinks it was impossible.

"Sir, I beg to report that the crew is/are debating the odds of a successful mutiny among themselves."

"Five cups of sugar is/are needed for the cake recipe!"

A shirt and shoes is/are required dresscode for most restaurants.

Although taking classes that challenge/challenges you can be hard, the benefits are often exponential - assuming you can avoid total failure.