—There is a lot of smoke coming out of the teaching-building there.
—Really?It _________ be a fire,most probably.
| A．can | B．ought to | C．have to | D．must |
It is _____ my father worked _____ I work now.
| A．where, that | B．where, when |
| C．that, where | D．that, that |
It is the protection for the trees _______ really matters, rather than how many trees are planted.
| A．what | B．that |
| C．不填 | D．which |
It is _______ he often fails in exams ______ makes his parents worried about him.
| A．what； that | B．that； what |
| C．that； that | D．/ ； that |
Who are making so much noise in the garden？
—_______ the children.
| A．It is | B．They are |
| C．That is | D．There are |
It was lack of money, not of effort, _____ defeated their plan.
| A．which | B．as |
| C．that | D．what |