1. We have to stay at home. The weather is bad.
2. You must (have to) tell your mother the truth.
3. Could you speak English when you were six?
4. I must (have to) go. It's late already.
Ответ:
l think 3D printer will improve our lives, because it can print fully-functional machines. This incredible invetional will transform our lives beyond our imagination.
2 не имеет смысла, т. к. корень из отриц. числа
У нас в России 3 месяца зимы