By serving others, a person focuses on someone other than himself or herself, ________ can be very eye-opening and rewarding.
| A．who | B．which |
| C．what | D．that |
The book was written in 1946, ____ the education system has witnessed great changes.
| A．when | B．during which | C．since then | D．since when |
I wish to thank Professor Smith, without ________ help I would never have got this far.
| A．who | B．whose |
| C．whom | D．which |
English is a language shared by several diverse cultures, _________ uses it differently.
| A．all of which | B．each of which | C．all of them | D．each of them |