D. Sandra should answer the easy questions first. Then she should go back and reevaluate the more difficult question.
This gives Sandra the best chance to do well. By answering the easier questions first, Sandra can be sure to answer the ones correctly that she is confident with. Sometimes this can then help the brain get into a groove and can help lead to answering questions that may have been seen as difficult earlier. When approaching the more difficult questions Sandra should be able to at least eliminate one answer choice. Even if she guesses, she will have increased her chances since she is choosing between three possibilities instead of just 2.