28. It is only when agriculture is fully developed___________industry can have abundant materials and markets.
| A．that | B．when | C．before | D．Until |
This is the very letter ____came last night.
| A．who | B．which | C．that | D．as |
I know only a little about this matter; you may ask ____ knows better than I.
| A．whoever | B．whomever | C．anyone | D．the one |
This is the school ____ we visited three days ago.
| A．where | B．/ | C．when | D．what |
This is the factory ____ we worked a year ago.
| A．where | B．that | C．which | D．on which |
Nearby were two canoes ____ they had come to the island.
| A．which | B．in which | C．that | D．/ |