Match the two parts of the sentences:
1. We all have...
2. Researchers have recently discovered...
3. A circadian period...
4. Your 'master clock'...
5. Cycles of sleep and wakefulness...

a. the plant cells contain biological clocks.
b. a type of 'inner alarm clock'.
c. works with your body's circadian rhythms.
d. affect our health and productivity.
e. is approximately 24 hours long.