=> 1. C No one knows exactly ( Dòng 2 đoạn 1 : Nobody knows exactly.....) 2. D. ( A and B are correct -> We have to start...alternative)
3. D ( Radioactivity causes cancer and may badly affect the future generations.) 4. C ( Dòng cuối đoạn 2 : we should use natural resources as economical as possible.)
5. B ( dòng đầu đoạn 2 : because it's very dangerous.)
