听下面一段材料，回答第1至4题。 1. What kind of passage have you just heard? [     ] A. A public lecture. B. A radio announcement. C. A government statement. 2. What is the main purpose of the event? [     ] A. To increase people's sense of environment protection. B. To invite people to join an environmental organization. C. To persuade families to have an outing in the mountains. 3. How many trees are going to be planted today? [     ] A. 7,000 B. 2,000 C. 4,000 4. What does the speaker advise volunteers to do? [     ] A. To learn some tree-planting skills. B. To come along any time they like. C. To bring along their gloves.