They improved communications despite tough circumstances， laid down important（）for the frontier’s development， and also made vital contributions to preserving the Union.
They improved communications despite tough circumstances， laid down important（）for the frontier’s development， and also made vital contributions to preserving the Union.
A、appreciation
B、infrastructure
C、link
D、innovative
正确答案：infrastructure
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时间：2023-10-07 15:10:42