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Scientists are always trying to solve the mysteries of the universe．These people use their various skills to investigate what, why, where, and how things happen．Two of the most important tools a scientist has are observation and experimentation．
Science always begins with observation．Careful observation always leads to questions．Then a hypothesis can be formed．However, a hypothesis is only useful if it can be tested.
The best way to test a hypothesis is to design an experiment．Each experiment is designed to answer one question only — is the hypothesis true or false? In nature, there are often too many variables to know why something happened．However, a scientist can limit the number of variables．
Although experiments are important, they aren't always practical．An astronomer can't travel across space, but with observation, he or she can still learn a lot about stars．For example, experiments on Earth have shown that when elements are burned, each one gives off a very specific colour．By observing the colours of stars, astronomers can tell which chemical elements the star contains.
Certain types of science use observation much more than experimentation．Archaeology, paleontology, and astronomy rely on observing the world, and then drawing conclusions based on the evidence．
Word List
investigate： try to find answers
hypothesis： an idea about why and how things happen
variables： possible reasons for things happening
You Practice
I．Answer the following questions.
1）Why are observation and experimentation both important?
2）Why can experiments often give clearer answers than nature?
3）Why is observation so important for an astronomer?
4）What is a hypothesis?
5）Why is it not always possible to conduct experiments?
II．Word power—Use these words from the reading in sentences of your own.
1）hypothesis ____________________
2）observation ____________________
3）variables ____________________
4）evidence ____________________
5）investigate ____________________
III．True / False / Not Given—Write W if the sentence is true, F if it is not true, or NG if there is no information about this sentence.
____ 1）Science begins with experimentation．
____ 2）A hypothesis tries to answer many questions．
____ 3）A hypothesis must be tested to be useful．
____ 4）In order to make observations, astronomers must travel through space．
____ 5）Part of a scientist's job is to limit the number of variables in an experiment．