Write the next sentence in the following story.

How to add fish to new tank
Wash the gravel, rocks, and ornaments.
Once you get your new tank and your tank additions, you will need to wash them in warm water. Do not use any soap or detergents to wash the gravel, rocks, or ornaments, just warm water.

Available options:
[a]. Scrub off any sand or rocks that is stuck to the gravel. Make sure to get down every inch of gravel so that the tank's water does not get contaminated..
[b]. Use the cold water to wash clean all the minerals on the gravel. Do not clean the gravel often as you will need it again soon..
[c]. If the water is very warm, add a few drops of salt or a few drops of baby oil in to the water. You can also use your finger to rub the salt on the gravel..
[d]. This will ensure these items are free of dirt, bacteria, and toxins. You can wash the gravel by placing it in a colander... The answer should be
[d].