This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to use home remedies to get rid of gnats
Let infested soil dry out.
Allow the top 2 inches (5 cm) of soil to dry out completely before watering a gnat-ridden plant again.
Eggs are usually laid in damp, over-watered plants, and gnat larvae need to develop in moist organic material.

a). Slice the gnat-infested soil out with a round knife. Do this carefully with enough force to break the sack.
b). Wait for the soil to dry out after watering to check if the soil is dry out properly. Begin by taking a small amount of diatomaceous earth (tsp).
c). Keep the soil moist and uncovered after watering, though, or the gnat-infested plants can stay up roots longer. Insecticides can be fatal to gnat larvae, and can permanently encourage disease.
d). Eggs and larvae will dry out and die if exposed to dry conditions. The infested plant may show early signs of withering, but this is unavoidable.
The answer is:
d).