THÌ & THỂ CỦA ĐỘNG TỪ - Chia các động từ trong ngoặc để hoàn thành câu. 1. Over the last one hundred years, the world temperature ___________________________ (rise) by 10C and this really worries scientists. 2. I ______________________________ (start) collecting stamps five years ago and so far I _________________________ (collect) over two hundred. 3. The nomadic child ___________________________ (fall) off the horse while he ___________________________ (ride) down a hill. 4. If this factory stops dumping untreated waste into the river, its water ______________________ (be) safe to drink again. 5. Our environment ___________________________ (pollute) so seriously if people were aware of the environmental protection