Fill in the verbs using them in the appropriate form.
1    In the twentieth century, scientists ... extracts of ancient plants in floating masses of
2    When travelling by car, be very attentive and ... dangerous driving.
3    Since the passengers were in danger, the rescue party used a helicopter to get to the place where two ships ....
4    The captain of the submarine ordered the crew to stop the engines to ... a collision with a strange unidentified object moving towards them under the water
5    An expedition of specially-trained divers have kept trying to find the ship that... more than half a century ago.
6    An unexpected storm seriously ... the ship. That's why the captain ordered them to stop in the nearest port to repair it.
7    This shipbuilding company has a long and successful history. They ... one or two liners every year.