Exercise 3. Match the antonyms.
1. begin
2. external
3. free of
4. artificial
5. divide
6. completely
7. necessary
8. straight
9. fission
10. action
a) internal
b) natural
c) end
d) combine
e) full of
f) unnecessary
g) partially
h) fusion
i) curved
j) reaction
k) motion
I) basic