Smart Thinker Answers Answers
4A
stylus
When sunlight shines on the stylus of a sundial, the stylus casts a shadow on the markings on the template. The shadow changes its position at different times, so people can tell the time from the sundial.
p.13
template
equatorial sundial
p.16 A leap year is a year that has 366 days, which is one day more than a common year. It appears to fill the gap between the number of days in a year set by humans (365 days) and the actual revolution cycle of the Earth (around 365.2422 days). Therefore, a leap year mostly happens every four years.
Any reasonable answers, e.g. the melting of sea ice makes people living in the North Pole hard to go to different places freely to hunt; it also makes animals unable to live, hunt for food and reproduce on sea ice, increasing their risk of death.
p.21
Any reasonable answers, e.g. arctic foxes and penguins, they also have thick fur and thick layers of fat.
p.31
Bats. They use little energy for the hanging posture. They hang themselves upside down during their deep sleep in winter too.
p.36 Mai Po Nature Reserve is located in the northwest of Yuen Long in the New Territories. World Wildlife Fund Hong Kong manages the reserve.
p.41 No. For example, elephants are plant-eating animals and they are bigger than tigers. Rabbits are plant-eating animals too, but they are smaller than tigers.
p.42 Any reasonable answers, e.g. Yes. It is because energy passes through the feeding relationships between living things. A food chain starts with a producer (plants). They absorb energy from sunlight to grow. Plant-eating animals eat plants to get energy. Then, meat-eating animals eat plant-eating animals to get energy. This shows that the energy of living things comes from the Sun. p.56 When a plant reproduces, changes may happen in the offspring, causing it to develop a different characteristic. For example, a camel's foot tree (with pink flowers) has once changed during reproduction, creating a new variety with white flowers of the same shape.
p.77 Any reasonable answers, e.g. some types of cancer, such as colorectal cancer, breast cancer and prostate cancer, may be related to heredity.
p.79 It is because heart diseases develop slowly, but the fat built up in the blood vessels of the heart cannot be removed easily. The situation will continue and may worsen. Although cardiovascular diseases are chronic diseases, people have the risk of heart attacks anytime.
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