The correct answer is $\boxed{\text{B}}$.
Humans have two sets of teeth: deciduous teeth (baby teeth) and permanent teeth. Deciduous teeth typically start to fall out between the ages of 6 and 12, and permanent teeth start to come in around the same time.
There are 20 deciduous teeth, 10 in each jaw. These teeth are smaller and less complex than permanent teeth. They are also not as firmly rooted in the gums, which is why they fall out more easily.
There are 32 permanent teeth, 16 in each jaw. These teeth are larger and more complex than deciduous teeth. They are also more firmly rooted in the gums, which is why they are less likely to fall out.
The four teeth that come out twice are the wisdom teeth. Wisdom teeth are the third molars, and they are the last teeth to come in. They usually start to come in between the ages of 17 and 25.
Wisdom teeth can sometimes cause problems, such as overcrowding, infection, and tooth decay. If wisdom teeth are causing problems, they may need to be removed.
The other options are incorrect because they do not represent the number of teeth that come out twice. Option A, 4, is the number of incisors in each jaw. Option C, 20, is the total number of deciduous teeth. Option D, 28, is the total number of permanent teeth.