— Have you ever come here before?

— No, it is the first time that I______ to this city.

[      ]

A. have been

B. had been

C. came

D. come

已知两个向量组α₁=(1，2，3)^T，α₂=(1，0，1)^T与β₁=(-1，2，t)^T，β₂=(4，1，5)^T。
(Ⅰ)t为何值时，两个向量组等价
(Ⅱ)两个向量组等价时，求出它们之间的线性表示式。