Directions: There are 10 blanks in the following passage.
For each numbered blank, there are 4 choices marked A, B, C and D. Choose the
best one and mark your answer on the ANSWER SHEET with a single line through the
center. The safety of ships at sea does not
depend only on the arrangements made in the ships themselves. Dangerous coasts
and rocks may be seen in the daytime, 1 they are a threat to safe navigation at night. Lighthouses are therefore
erected at such places to 2 sailors of
the danger. Modern lighthouses are put up at all dangerous places near the
courses 3 by ships. On some rocky
coasts several lighthouses may be built not far from each other, and 4 the sailors on a ship may know which is which,
they have 5 arrangements of lights. One
lighthouse will give a single flash at regular 6
, another may give two flashes; a third may give two followed by
one; and so on. 7 watching the lights
the navigator is able to decide exactly where he is, and he can set his
8 with confidence. In the approaches to
some ports two continuous lights are set up, one above
9 but some distance behind; when they appear from the sea
one above the other, the ship is on the right course; but if they do not, the
captain knows that he is 10 his course
and likely to strike a rock or the bottom of the sea.