Multiple Choice, Multiple Answers

Read the passage and select ALL statements it supports.

Before satellite navigation, lighthouses were vital guardians of dangerous coastlines. A revolving lamp at the top of a tall tower warned ships away from hidden rocks and shallow waters. The real breakthrough came in the early nineteenth century with a special stepped lens that bent scattered light into a single powerful beam, allowing a modest flame to be seen many kilometres out at sea. Each lighthouse was given its own pattern of flashes, so that a captain could identify exactly which light he was passing simply by timing the intervals of darkness. Keepers once lived on site to tend the lamp, but most stations are now fully automated.