Let "a(t)" be a smooth function of "t" in "R^(n×n)," and assume "a(t′)a(t) = a(t)a(t′)" for all "t" and "t′." What does this imply about "a(t)"?
a) "a(t)" is a constant matrix.
b) "a(t)" is a diagonal matrix.
c) "a(t)" is a symmetric matrix.
d) "a(t)" is an antisymmetric matrix.