They talked for about an hour of things and persons _____ they remembered in the factory.
A. which
B. that
C. who
D. whom
We are going to spend this Spring Festival in Beijing, _____ live our grandparents and some relatives.
A. which
B. that
C. who
D. where
There are many areas in the world _____ lack experienced doctors.
A. where
B. in which
C. which
D. what
The years and months _____ we spent together are really wonderful to us all.
A. when
B. on which
C. in which
D. that