如图，已知白纸上有一椭圆\(C\)，它焦点为\(F _{1}\)，\(F _{2}\)，长轴\(A _{1} A _{2}\)，短轴\(B _{1} B _{2}\)，\(P\)是椭圆上一点，将白纸沿直线\(B _{1} B _{2}\)折成\(90°\)角，则下列正确的是\((\:\:\:\:)\)
①当\(P\)在\(B _{1} (\)或\(B _{2} )\)时，\(PF _{1} +PF _{2}\)最大．
②当\(P\)在\(A _{1} (\)或\(A _{2} )\)时，\(PF _{1} +PF _{2}\)最小．