Question

to make salt water a heterogeneous mixture, you would have to
a add sand.
b add a small amount of sugar.
c boil the water.
d remove the salt.

Explanation:

A heterogeneous mixture has visibly different substances. Salt water is a homogeneous mixture (uniform). Adding sand (which doesn't dissolve uniformly) makes it heterogeneous. Sugar (like salt) dissolves (homogeneous). Boiling water just changes state (still homogeneous if salt remains). Removing salt makes it water (homogeneous).

Answer:

A. add sand.