We can make electricity from tidal energy by:

• A. using floating platforms that go up and down with the tide
• B. moving equipment up and down a beach
• C. damming off a large coastal bay where the water flows in and out
• D. installing windmills
• E. none of these

A river is usually exploited to provide electrical power (energy) by:

• A. steepening its channel so it flows faster
• B. catching and removing solid objects being carried along by the flow

C. building a dam

• D. installing a set of vanes like a boat's paddle-wheel to be turned by the flow
• E. A and D