根据语境或句意，用所给词的正确形式填空。

86. 1. In China it's ____  (polite)to stick your chopsticks into your food when you eat.
    
87. 2. My teachers always encourage us ____  (study)hard on different subjects.
    
88. 3. Jenny brought two nice____ (picture)of her family to school yesterday.
    
89. 4. The library is between the school and the hospital. You can find it ____  (easy)
    
90. 5. While I ____   (wait)for the bus at the bus station,it began to rain.