Li Na returned to Wuhan after the Games,________, as is known to us, she had been brought up and

trained to be a gold medalist of tennis.[ ]

A. when  

B. that  

C. there  

D. where

已知α₁，α₂，α₃是3维向量空间V的一组基，设β₁=α₁，β₂=α₂+α₃，β₃=aα₁+α₂-α₃．

求β₁，β₂，β₃到α₁，α₂，α₃的过渡矩阵；