4.[单选题] lim _(xarrow 1)dfrac ({x)^2-t-1-t}({x)^2-2t}= ().()-|||-A dfrac (3-i)(4)i;-|||-B) dfrac (3+i)(4)i;-|||-C dfrac (1-3i)(4);-|||-D dfrac (1+3i)(4).