Many stars are i__________ without a telescope.
Try to be more __________(积极)in dealing with the problem.
A __________(激烈的)debate on the tax cut was going on.
If the sun were to __________(消失),what would the earth be like?
These teaching materials can be __________(改编)for older children.
Mr Smith __________ __________ __________ attend the meeting because he is too busy. (不可能)