现在进行时表原因 — 英语词汇题
题目
根据中文提示或首字母补全句子，使句意完整：1. The park is dirty b______ some people ______ ( litter, 正在乱扔垃圾 ) on the grass. 2. The air is bad today because a car ______ ______ ( smoke, 正在冒烟 ) near our school. 3. Look! The buses are ______ ( stop, 正在停下 ) because the road is blocked. 用所给动词的正确形式填空，注意根据句意判断何时用现在进行时。