(1 point) a is an m×n matrix. check the true statements below:

a. the column space of a is the range of the mapping x→ax.

b. the null space of a is the solution set of the equation ax=0.

c. col(a) is the set of all vectors that can be written as ax for some x.

d. the kernel of a linear transformation is a vector space.

e. the null space of an m×n matrix is in rm.

f. if the equation ax=b is consistent, then col(a) is rm.