I admit that all these problems are difficult, I don’t agree that they cannot be solved.
A. Unless
B. While
C. Until
D. Since
网友回答
A. Unless
(答案→)B. While
C. Until
D. Since
解析：考查连词辨析。A除非，如果…不；B当…时；然而；可是；尽管；C直到…才…;D自从，既然；句意：尽管我承认所有的问题都很难，但是我不同意他们都不能被解决。故B正确。