Before reading any further, take some time to learn the directions cold. Some of the wording in the directions below has been changed from the GMAT to make it clearer. That is, there are no complex numbers. You can assume that a line that appears straight is straight and that angle measures cannot be zero. You can assume that the relative positions of points, angles, and objects are as shown.
All drawings lie in a plane unless stated otherwise.
Hence, the answer is C. Notice in the above example that the triangle appears to be a right triangle. You must be very careful not to assume any more than what is explicitly given in a Data Sufficiency problem. In fact, it is rare that you won't be able to eliminate some answer-choices. Remember, if you can eliminate at least one answer choice, the odds of gaining points by guessing are in your favor. The following table summarizes how elimination functions with Data Sufficiency problems.