Let v1,...,vn be vectors in an n-dimensional vector space V. Select each answer that must always be true. Explain your reasons.
(a) if m ≤ n, then v1,...,vn are linearly independent.
(b) if v1,...,vn span V, then m ≥ n.
(c) if v1,...,vn are linearly dependent, then v1 must be a linear combination of the other vectors.
(d) if m = n and v1,...,vn span V, then v1,...,vn are linearly independent.