A 31-year-old man complains about dryness, burning of tongue dorsum that appeared for about a week ago and is getting worse during eating stimulating food. Some time ago the patient had pneumonia. He spent two weeks at a hospital, was taking antibiotics. He doesn’t take any drugs at the moment. Objectively: mucous membrane of oral cavity is hyperemic, dry and glossy. On the tongue dorsum and palate some greyishwhite films are present that can be easily removed. Threads of saliva follow the spatula. What is the most probable provisional diagnosis?