B11

A recent study may have an answer to one of the greatest unsolved mysteries in science — what is the purpose of sleep? The work suggests it’s really about making animals function more efficiently in their environments.

 REAL

B12

Scientists from the University of California, Los Angeles, conducted a study of the sleep times of a broad range of animals. They discovered much variation.

 SCIENCE

B13

You may think it impossible but some migrating birds canfly non-stop for up to 90 hours.

 POSSIBLE

B14

Pythons and bats are among the longest sleepers at over 18 hours a day.

 SLEEP

B15

Human babies need 16 hours and their health and intellectual development depend on sleeping properly.

 DEVELOP

B16

Most of us probably feel we need around eight hours sleep to function well. Some people have difficulty/difficulties in getting enough sleep and this may lead to serious health problems.

DIFFICULT