What do you think can be done _(keep) the miners safe?

题目

What do you think can be done _(keep) the miners safe?
What _(happen) to the forest in China in the last 10 years?
Is that signture in your h_?
The l_ ring was never found.

答案

What do you think can be done (to keep) the miners safe?
What (has happened) to the forest in China in the last 10 years?
Is that signature in your (hand)?
The (lost,丢失的) ring was never found.