If you were bringing friends home to visit, you could show them the way. You know the landmarks—a big red house or a bus-stop sign. But what if you were swimming in the middle of the Atlantic Ocean? Could you still find your way home? A loggerhead turtle（海 龟）could.
According to Dr. Ken Lohmann, loggerheads have a magnetic（磁力的）sense based on Earth’s magnetic field. It helps them locate the best spots for finding food and their home beaches.
Scientists already know that several other animals, such as whales and honeybees, can detect（探测到）magnetic fields. The difference between them and loggerheads, however, is the way they learn to use their magnetic sense. Young whales and honeybees can learn from adults. Loggerheads are abandoned as eggs.
As newborn loggerheads have no adults to learn from, what helps them figure out how to use their magnetic sense? Lohmann thinks one of the cues was light on the sea.
Baby loggerheads hatch only at night. However, a small amount of light reflects off the ocean. The light makes that region brighter. Heading toward the light helps them get quickly out to sea, where they can find food. Lohmann tested whether newborn loggerheads use this light source to set their magnetic “compasses”（罗盘）. He and his team put some newborns in a water tank and recorded which way they swam. Around the tank, the scientists created a magnetic field that matched the Earth’s. They set a weak light to the east of the magnetic field. Then they let the newborns go.
At first, the newborns swam toward the light. After the scientists turned off the light, the turtles that had seen the light in the east always swam toward east. When the researchers reversed（颠倒）the magnetic field, these turtles turned around and swam toward the new “east”.
This and the follow-up experiments all showed that loggerheads use light from the outside world to set their magnetic “compasses” and then remember the “correct” direction. If a turtle hatches on a brightly-lit beach, that would damage its magnetic sense forever and make survival hard for the turtle.
Lohmann’s work has led others to protect the habitat of this endangered species. Yet many questions about these creatures remain unanswered, and researchers have a lot to study.
28．What is needed for newborn loggerheads to set their magnetic sense?
A．Weak light reflected off the ocean. B．Help from adult loggerheads.
C．Bright sunlight from the sky. D．Food in warmer waters.
29．In the experiment, after the newborns’ magnetic sense was set, their moving direction was determined by ____.
A．the light                       B．the magnetic field
C．other unknown factors           D．the light and the magnetic field
30．What is the significance of Lohmann’s research work?
A．It enables researchers to keep track of turtles.
B．It contributes to the studies of the magnetic field.
C．It offers a new solution to environmental pollution.
D．It helps protect the loggerheads’ living environment.
31．What could be the best title of the passage?
A．Experiments on Loggerheads         B．The Survival of the Sea Turtle
C．The Loggerhead’s Built-in “Compass”  D．Comparison of Loggerheads and Other Animals

28-31 ABDC