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Consider the following statements:

In a nuclear reactor, self-sustained chain reaction is possible, because

1. more neutrons are released in each of the fission reactions.

2. the neutrons immediately take part in the fission process.

3. the fast neutrons are slowed down by Graphite.

4. every neutron released in the fission reaction initiates further fission.

Which of these statements are correct?

A)  1, 2 and 3                    

B)  1 and 3

C)  2 and 4           

D)  2, 3 and 4