Correct Answer: (e) None of the above
Solution:A lock is a device used for raising and lowering boats, ships and other watercraft between stretches of water of different levels on river and canal waterways. Locks are used to make a river more easily navigable or to allow a canal to take a reasonably direct line across land that is not level. According to the question, in given options, the lock system has been applied in the Panama Canal, the Danube river and the Rhine river while it is not used in the Suez Canal.