Solar energy production has made huge strides in recent years, __16.__ advances inphotovoltaic technologies—the underpinnings of solar panels—have made it easier and cheaper toharness energy from the sun. But there are still challenges regarding how to store the energyharvested by solar panels. If we could convert solar energy into a liquid form, though, it becomesmuch easier to store and transport. Now, a group based at UNC-Chapel Hill has __17.__ a hugegrant from the U.S. Department of Energy to advance research on new designs to convert sunlight 
 into storable fuels. If scientists could __18.__ the process in photosynthesis, and produceelectricity stored as a liquid fuel, it could potentially be used in combustion engines and fuel cells.The process is called artificial photosynthesis, and scientists have made some notable successes__19.__ all contained in the lab. Nonetheless, the technology may not be far away from becominga reality. If this so-called solar thermal fuel can be perfected, it might __20.__ of fossil fuels.
【題組】16.
(A) unless
(B) while
(C) as
(D) despite