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
正确答案：C
答案解析：这部分所说的体积的减小和所需时间的缩短恰好与前半句中提到的冰箱大小的体积和所需数分钟的时间形成了对比。即：目前它大约像冰箱那么大，而且要用几分钟扫描一个电路，但是他们正在努力使它缩小到台式计算机那么大，把扫描时间缩短到30秒。