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

How to clean your scalp
Use a clarifying shampoo.
Once a month, you should wash your hair with a clarifying shampoo. Leave the clarifying shampoo on your scalp for three minutes (or just follow the instructions on your shampoo).

Choose from:
[a]. Wash the sulfates out of your hair with cold water. Some people can also use a natural scalp moisturizer for temporary hair care.;
[b]. Rinse your hair as often as needed, until all the shampoo is off. Some clarifying shampoos may require a quick rinse, but the results will always be the same for every time.;
[c]. Then use a hot tub to wash your scalp. Remember to keep your hair out of the shower for only thirty seconds and use plenty of water.;
[d]. This will help remove buildup and dead skin cells. Clarifying shampoos can strip hair color, so use them before you get your color done again.;
The answer is:
[d].