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1. Don’t talk about such things of _______ you are not sure.
A. which
B. what
C. as
D. those
2. The wolves hid themselves in the places __________ couldn’t be found.
A. that
B. where
C. in which
D. in that
3. The freezing point is the temperature __________ water changes into ice.
A. at which
B. on that
C. in which
D. of what
4. This book will show you __________ can be used in other contexts..
A. how you have observed
B. what you have observed
C. that you have observed
D. how that you have observed
5. The reason is __________ he is unable to operate the machine.
A. because
B. why
C. that
D. whether
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