Two years ago, three scientists traveled to the Antarctica to explore a secret world hidden _________ the ice.
To improve their oral English, everyone in the class is supposed to ________ actively in these discussions.
The ________ soldier said it was ________ to give up his rest time to save more people caught in the earthquake.
________ Yao Ming has retired from the NBA, the pleasure we have got by watching him play basketball at home and abroad will last long.
People have the belief ______ factories should produce fewer things from raw materials, ______ the supply is growing smaller and smaller.
The man is such a ________ person that there is no doubt that he will do whatever he has promised.