Перепишите следующие предложения; подчеркните в каждом из них модальный глагол или его эквивалент и определите его видовременную форму.
1. Energy can exist in many forms.
2. The chemists may use the reactor to analyse various substances.
3. The engineer will have to explain this difficulty.
4. You should follow all the important scientific researches in your field.
5. He had to investigate a series of accidents.