a basis for the null space of a is { <0,0,0,0> }. you should be able to explain and justify your answer. enter a coordinate vector, such as <1,2,3,4>, or a comma separated list of coordinate vectors, such as <1,2,3,4>,<5,6,7,8>. the dimension of the null space of a is because (select all correct answers -- there may be more than one correct answer): a. rref(a) has one free variable column. b. rref(a) has a pivot in every row. c. rref(a) has two free variable columns. d. three of the four columns in rref(a) have pivots. e. rref(a) is the identity matrix. f. the basis we found for the null space of a has two vectors. g. two of the four columns in rref(a) do not have a pivot.