单选题

　　[填句补文] Although the researchers have only just made the technical details of the microscope public， it is already on sale. It is currently the size of a refrigerator and takes several minutes to scan a circuit， but Xiao and Schrag are working ________.

　　A.to take tiny chips we require

　　B.to making chips any smaller

　　C.to shrink it to the size of a desktop computer and cut the scanning time to 30 seconds

　　D.of conducting electricity