Where are the Sentence Completion Questions?: Sentence completion questions appear in all three Critical Reading sections of the SAT I.
How Many are There?: Overall, there are 19 sentence completion questions in every SAT I. Usually this number is divided between the Critical Reading sections so that there is a set of 8, 5, or 6 sentence completions in each section. They compose about a third of all of the Critical Reading questions.
Are They all the Same?: No - there is a clear progression in difficulty in each set of sentence completion questions. The first will be the easiest, and the difficulty increases such that the last question of each set will be the hardest.
What Skills are Required?: Every sentence completion question will test your vocabulary, so a strong vocabulary helps. You will also need to demonstrate that you understand complex sentence structures.
How to Prepare: Spend some time on vocabulary, some time on learning strategy, and some time on putting strategy to practice by answering sample questions.