Scientists have （） for years that turbulence within the gaseous clouds found throughout the Milky Way stymies star formation, but some of the forces behind this disturbance remain （）.

The vireo's comeback may prove that habitat along strea...

单项选择题The vireo's comeback may prove that habitat along streams in Southern California is recovering from the effects of pollution,（） indicator of environmental health in a state that has lost most of its （） woodlands.

His specialty is bringing to the forefront the strange ...

单项选择题His specialty is bringing to the forefront the strange and （） acts of depravity that only the impassive and imperturbable subconscious is （） to grasp and reckon with.

If a particular vaccine is produced only by one company...

单项选择题If a particular vaccine is produced only by one company at a single facility, there is a possibility that the supply of vaccine could grow （） if the company decides to cease production.