I admit that all these problems are difficult I don’t agree that they cannot be solved.A

问题补充：

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

答案：

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。