Suponiendo que estás usando el presente simple y el pasado simple, las respuestas quedarĂan de la siguiente manera:
1. When my gradfather uses a cell phone, he feels fascinated.
2. Nowadays computers are small but in 1900 computers were enormous.
3. In 1900 people loved to listen to the radio.
4. In 1900 people believed that virtual reality was impossible.
