6. He had thousands of students, many of ______ gained great success in their own field.
| A．whom | B．them | C．which | D．who |
I met the fruit-pickers, several of _______ were still university students.
| A．that | B．who | C．them | D．whom |
Her sons, both of ______ work abroad, will come back home this summer.
| A．that | B．who | C．them | D．whom |
George, with _______ I played tennis on Sundays, was a warm-hearted person.
| A．that | B．him | C．them | D．whom |
（3） This I did at nine o’clock, after _______ I sat reading the paper.
| A．that | B．it | C．them | D．which |