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用數學歸納法證明“(n+1)(n+2)·…·(n+n)=2ⁿ·1·3·…·(2n-1)”,從“k到k+1”左端需增乘的代數式為(    )

A.2k+1                           B.2(2k+1)

C.                         D.

用數學歸納法證明“(n+1)(n+2)·…·(n+n)=2ⁿ·1·3·…·(2n-1)”,從“k到k+1”左端需增乘的代數式為(    )

A.2k+1              B.2(2k+1)               C.            D.

用數學歸納法證明“(n+1)(n+2)…(n+n)=2ⁿ·1·3·…·(2n-1)(n∈N)時”,從“n=k到n=k+1”,左邊需增乘的代數式是(　　)

A.2k+1                  B.              C.2(2k+1)             D.

用數學歸納法證明“(n+1)(n+2)…(n+n)=2ⁿ·1·3·…·(2n-1)(n∈N)時”,從“n=k到n=k+1”,左邊需增乘的代數式是(　　)

A.2k+1                  B.              C.2(2k+1)             D.

用數學歸納法證明:(n+1)(n+2)…(n+n)=2ⁿ·1·3·…·(2n-1),其中n∈N^*.