24．Progress _________ so far very good and he is sure that his new book will be finished on time．
| A．was | B．had been | C．has been | D．will be |
I saw some trees the leaves of _____ were black with disease.
| A．that | B．which | C．it | D．what |
Their problem today is somewhat similar to _____ they faced many years ago.
| A．that | B．which | C．that which | D．it |
Dorothy was always speaking highly of her role in the play, ____, of course, made the others unhappy.
| A．who | B．which | C．this | D．what |
He made another wonderful discovery, ______ of great importance to science.
| A．which I think is | B．which I think it is | C．which I think it | D．I think is |
He’s got himself into a dangerous situation _____ he is likely to lose control over the plane.
| A．where | B．which | C．while | D．why |