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 ________ we admit that there are still some problems about the system of modern education,

we don’t mean that it is of no use.

A. Until           B. While                C. As                    D. Unless

1.   _______ we admit that there are still some problems about the system of modern education, we don’t mean that it is of no use.

A. Until     B. While           C. As            D. Unless

 ________ we admit that there are still some problems about the system of modern education,

we don’t mean that it is of no use.

A. Until         B. While              C. As                  D. Unless

_______ we admit that there are still some problems about the system of modern education, we don’t mean that it is of no use.

A. Until     B. While           C. As            D. Unless

_________ we admit that there are still some problems about the system of modern education, we don't mean that it is of no use.

A. Until　　　 B. While　　　　　 C. As　　　　　　 D. Unless