选出下列每组单词中不同类的一项。
(______) 1. A. doctor B. blackboard C. nurse D. teacher
(______) 2. A. pupil B. student C. teacher D. desk
(______) 3. A. ruler B. eraser C. football D. pencil
(______) 4. A. throw B. apple C. pear D. grape
(______) 5. A. good B. useful C. dirty D. draw