6. The freezing point is the temperature __________ water changes into ice.
A. at which
B. on that
C. in which
D. of what
7. 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
8. The reason is __________ he is unable to operate the machine.
A. because
B. why
C. that
D. whether
9. I’ll tell you __________ he told me last week.
A. all which
B. that
C. all that
D. which
10. That tree, __________ branches are almost bare, is very old.
A. whose
B. of which
C. in which
D. on which
其中第8题is后面的是定语从句还是表语从句，还有第9题，一定要加个all才行吗