Known as "Senegal's best pupil" and very popular in her home country, Diary Sow has not been seen or heard from since January 4. An inquiry has been opened in France, where Sow is a student at Paris's prestigious Lycée Louis-le-Grand, into her troubling disappearance. The 20-year-old is in her second year at the elite French preparatory school in central Paris. She did not appear after the Christmas break. "She is a punctual pupil, very serious,...