3. Our grandparents not be as familiar with technology in their childhood as we are now.
В данном предложении нужно использовать глагол to be в форме прошедшего времени (Past Simple) во множественном числе (grandparents) в отрицательной форме.
Our grandparents were not as familiar with technology in their childhood as we are now.
Ответ: were not