. Enough attention should be paid to _____ your pronunciation and intonation.
| A．improve | B．improving | C．improved | D．be improve |
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 |