The reform in economic system will help（）and develop the socialist economic base.

单项选择题This is an illness that can result in total blindness（）left untreated.

A. after
B. if
C. since
D. unless

单项选择题The physicist has made a discovery, （） of great importance to the progress of science and technology.

A. I think which is
B. that I think is
C. which I think is
D. which I think it is