根据句意,用所给单词的适当形式填空。
| develop, produce, die, spit, pollute |
71. Can you see the sign “No ________” over there?
72. Air ________ is the most serious problem at the moment.
73. As we know, China is still a ________ country in the world.
74. Jane felt frightened (害怕) as soon as she saw the ________ snake.
75. Do you know America is one of the world’s largest ________ of oil?