1. If the vectors MA-→, MB-→, MC-→ do not coincide with each other and there is no three-point * * line, and the following relationship is satisfied (O is any point in space), the condition that the vectors MA-→, MB-→, MC-→ can become a set of bases in space is (c).

(A)OM―→= 13OA ―→+ 13OB ―→+ 13OC―→

(B)MA―→≠MB―→+MC―→

(C)OM―→=OA―→+OB―→+OC―→

(D)MA―→=2MB―→-MC―→

Analysis: judge whether three vectors form the basis of a vector, that is, judge whether these three basis vectors are * * * planes. If Ma-→, MB-→ and MC-→ are not * * planes, then points M, A, B and C are not * * planes. In option A, the four points A, B, C and M may be * *. In option B, it can only be explained that the vectors MA-→ are not MB-→ and MC-→ form a diagonal of a parallelogram, and the four points A, B, C and M may be * * * planes; Option d indicates that MA-→ is the diagonal of the parallelogram formed by vectors 2MB-→ and MC-→, then A, B, C and M are four * * * planes.

. 8. As shown in the figure, in the parallelepiped ABCDA1b1c1d, e and f are on B 1B and D 1D respectively, and be =13bb/d.

(1) Prove: A, E, C 1, F four-point * * * plane;

(2) If ef-→ = XAB-→+YAD-→+ZAA 1-→, find the value of X+Y+Z y+z. 。